Production of ionic liquids

ABSTRACT

Ionic liquids and processes and apparatus for their production. The ionic liquids can be low sulfur and low halide carboxylated ionic liquids. The ionic liquids can be produced via formation of at least one intermediate carboxylated ionic liquid, and thereafter subjecting the intermediate carboxylated ionic liquid to at least one anion exchange process.

RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional Pat. App. Ser. No. 60/901,615, titled “ESTERIFICATION OF CELLULOSE DISSOLVED IN CARBOXYLATED IONIC LIQUIDS,” filed Feb. 14, 2007, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to cellulose esters and/or ionic liquids. One aspect of the invention concerns processes for producing cellulose esters in ionic liquids.

2. Description of the Related Art

Cellulose is a β-1,4-linked polymer of anhydroglucose. Cellulose is typically a high molecular weight, polydisperse polymer that is insoluble in water and virtually all common organic solvents. The use of unmodified cellulose in wood or cotton products, such as in the housing or fabric industries, is well known. Unmodified cellulose is also utilized in a variety of other applications usually as a film (e.g., cellophane), as a fiber (e.g., viscose rayon), or as a powder (e.g., microcrystalline cellulose) used in pharmaceutical applications. Modified cellulose, including cellulose esters, are also utilized in a wide variety of commercial applications. Cellulose esters can generally be prepared by first converting cellulose to a cellulose triester, then hydrolyzing the cellulose triester in an acidic aqueous media to the desired degree of substitution (“DS”), which is the average number of ester substituents per anhydroglucose monomer. Hydrolysis of cellulose triesters containing a single type of acyl substituent under these conditions can yield a random copolymer that can consist of up to 8 different monomers depending upon the final DS.

Ionic liquids (“ILs”) are liquids containing substantially only anions and cations. Room temperature ionic liquids (“RTILs”) are ionic liquids that are in liquid form at standard temperature and pressure. The cations associated with ILs are structurally diverse, but generally contain one or more nitrogens that are part of a ring structure and can be converted to a quaternary ammonium. Examples of these cations include pyridinum, pyridazinium, pyrimidinium, pyrazinium, imidazolium, pyrazolium, oxazolium, triazolium, thiazolium, piperidinium, pyrrolidinium, quinolinium, and isoquinolinium. The anions associated with ILs can also be structurally diverse and can have a significant impact on the solubility of the ILs in different media. For example, ILs containing hydrophobic anions such as hexafluorophosphates or triflimides have very low solubilities in water while ILs containing hydrophilic anions such chloride or acetate are completely miscible in water.

The names of ionic liquids can generally be abbreviated. Alkyl cations are often named by the letters of the alkyl substituents and the cation, which are given within a set of brackets, followed by the abbreviation for the anion. Although not expressively written, it should be understood that the cation has a positive charge and the anion has a negative charge. For example, [BMIm]OAc indicates 1-butyl-3-methylimidazolium acetate, [AMIm]Cl indicates 1-allyl-3-methylimidazolium chloride, and [EMIm]OF indicates 1-ethyl-3-methylimidazolium formate.

Ionic liquids can be costly; thus, their use as solvents in many processes may not be feasible. Despite this, methods and apparatus for reforming and/or recycling ionic liquids have heretofore been insufficient. Furthermore, many processes for producing ionic liquids involve the use of halide and/or sulfur intermediates, or the use of metal oxide catalysts. Such processes can produce ionic liquids having high levels of residual metals, sulfur, and/or halides.

SUMMARY OF THE INVENTION

One embodiment of the present invention concerns a process for making a carboxylated ionic liquid. The process of this embodiment comprises: contacting an alkyl amine formate ionic liquid with an anhydride under conditions sufficient to convert the alkyl amine formate ionic liquid into the carboxylated ionic liquid via anion exchange. The carboxylated ionic liquid contains sulfur in an amount less than 200 ppmw and halides in an amount less than 200 ppmw.

Another embodiment of the present invention concerns a process for making a carboxylated ionic liquid. The process of this embodiment comprises: contacting an alky amine formate ionic liquid with at least one carboxylate anion donor to thereby produce the carboxylated ionic liquid. The carboxylated ionic liquid comprises sulfur in an amount less than 200 ppmw, halides in an amount less than 200 ppmw, and transition metals in an amount less than 200 ppmw.

Yet another embodiment of the present invention concerns an ionic liquid comprising a plurality of cations and a plurality of anions. In this embodiment, at least a portion of the anions are carboxylate anions, and the carboxylated ionic liquid comprises sulfur in an amount less than 200 ppmw, halides in an amount less than 200 ppmw, and transition metals in an amount less than 200 ppmw.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram depicting the majors steps involved in a process for producing cellulose esters in ionic liquids;

FIG. 2 is a more detailed diagram of a process for producing cellulose esters, depicting a number of additional/optional steps for enhancing to overall efficacy and/or efficiency of the process;

FIG. 3 is a plot of absorbance versus time showing the dissolution of 5 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 4 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 5 molar equivalents of acetic anhydride;

FIG. 5 is a plot of absorbance versus time showing the dissolution of 5 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 6 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride at 80° C.;

FIG. 7 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride and 0.2 molar equivalents of methane sulfonic acid at 80° C.;

FIG. 8 is a plot of absorbance versus time showing the dissolution of 5 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 9 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride and 0.2 molar equivalents of methane sulfonic acid at 80° C.;

FIG. 10 is a plot of absorbance versus time showing the dissolution of 10 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 11 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride and 0.2 molar equivalents of methane sulfonic acid at 80° C.;

FIG. 12 is a plot of absorbance versus time showing the dissolution of 15 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 13 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride and 0.2 molar equivalents of methane sulfonic acid at 100° C.;

FIG. 14 is a plot of absorbance versus time showing the dissolution of 15 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 15 is an NMR spectra showing the proton NMR spectra of a cellulose acetate prepared by direct acetylation;

FIG. 16 is plot of weight percent acetic acid versus time as determined by infrared spectroscopy;

FIG. 17 is a plot of absorbance versus time showing the removal of water from 1-butyl-3-methylimidazolium acetate prior to dissolution of cellulose;

FIG. 18 is a plot of absorbance versus time showing the dissolution of 10 weight percent cellulose in 1-butyl-3-methylimidazolium acetate at room temperature;

FIG. 19 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium acetate with 5 molar equivalents of acetic anhydride and 0.1 molar equivalents of zinc acetate;

FIG. 20 is a spectral analysis showing infrared spectra of 1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazolium acetate, a spectrum after 0.5 molar equivalents of acetic anhydride has been added to the 1-butyl-3-methylimidazolium formate, and a spectrum after another 0.5 molar equivalents of acetic anhydride has been added to the 1-butyl-3-methylimidazolium formate;

FIG. 21 is a plot of relative concentration versus time for 1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazolium acetate upon first and second additions of 0.5 molar equivalents of acetic anhydride;

FIG. 22 is spectral analysis showing infrared spectra of 1-butyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium formate, and a spectrum after 1 equivalent of acetic anhydride has been added to the 1-butyl-3-methylimidazolium formate in the presence of 2 molar equivalents of methanol;

FIG. 23 is a plot of relative concentration versus time for 1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazolium acetate upon addition of 2 molar equivalents of methanol and then upon addition of 1 equivalent of acetic anhydride;

FIG. 24 is a plot of absorbance versus time showing the dissolution of cellulose in 1-butyl-3-methylimidazolium acetate at 80° C.;

FIG. 25 is a plot of absorbance versus time showing the esterification of cellulose dissolved in 1-butyl-3-methylimidazolium acetate;

FIG. 26 is a spectral analysis showing the ring proton resonances for cellulose acetates prepared from cellulose dissolved in 1-butyl-3-methylimidazolium acetate (top spectrum), and the ring proton resonances for cellulose acetates prepared from cellulose dissolved in 1-butyl-3-methylimidazolium chloride (bottom spectrum); and

FIG. 27 is a spectral analysis showing the ring proton resonances for cellulose acetates prepared from cellulose dissolved in 1-butyl-3-methylimidazolium acetate after water addition (top spectrum) and before water addition (bottom spectrum).

DETAILED DESCRIPTION

FIG. 1 depicts a simplified system for producing cellulose esters. The system of FIG. 1 generally includes a dissolution zone 20, an esterification zone 40, a cellulose ester recovery/treatment zone 50, and an ionic liquid recovery/treatment zone 60.

As shown in FIG. 1, cellulose and an ionic liquid (“IL”) can be fed to dissolution zone 20 via lines 62 and 64, respectively. In dissolution zone 20, the cellulose can be dissolved to form an initial cellulose solution comprising the cellulose and the ionic liquid. The initial cellulose solution can then be transported to esterification zone 40. In esterification zone 40, a reaction medium comprising the dissolved cellulose can be subjected to reaction conditions sufficient to at least partially esterify the cellulose, thereby producing an initial cellulose ester. An acylating reagent can be added to esterification zone 40 and/or dissolution zone 20 to help facilitate esterification of the dissolved cellulose in esterification zone 40.

As illustrated in FIG. 1, an esterified medium can be withdrawn from esterification zone 40 via line 80 and thereafter transported to cellulose ester recovery/treatment zone 50 where the initial cellulose ester can be recovered and treated to thereby produce a final cellulose ester that exits recovery/treatment zone 50 via line 90. A recycle stream is produced from cellulose ester recovery/treatment zone 50 via line 86. This recycle stream can comprise an altered ionic liquid derived from the ionic liquid originally introduced into dissolution zone 20. The recycle stream in line 86 can also include various other compounds including byproducts of reactions occurring in upstream zones 20,40,50 or additives employed in upstream zones 20,40,50. The recycle stream in line 86 can be introduced into ionic liquid recovery/treatment zone 60 where it can be subjected to separation and/or reformation processes. A recycled ionic liquid can be produced from ionic liquid recovery/treatment zone 60 and can be routed back to dissolution zone 20 via line 70. Additional details of the streams, reactions, and steps involved in the cellulose ester production system of FIG. 1 are provided immediately below.

The cellulose fed to dissolution zone 20 via line 62 can be any cellulose known in the art that is suitable for use in the production of cellulose esters. In one embodiment, the cellulose suitable for use in the present invention can be obtained from soft or hard woods in the form of wood pulps, or from annual plants such as cotton or corn. The cellulose can be a β-1,4-linked polymer comprising a plurality of anhydroglucose monomer units. The cellulose suitable for use in the present invention can generally comprise the following structure:

Additionally, the cellulose employed in the present invention can have an α-cellulose content of at least about 90 percent by weight, at least about 95 percent by weight, or at least 98 percent by weight.

The cellulose fed to dissolution zone 20 via line 62 can have a degree of polymerization (“DP”) of at least about 10, at least about 250, at least about 1,000, or at least 5,000. As used herein, the term “degree of polymerization,” when referring to cellulose and/or cellulose esters, shall denote the average number of anhydroglucose monomer units per cellulose polymer chain. Furthermore, the cellulose can have a weight average molecular weight in the range of from about 1,500 to about 850,000, in the range of from about 40,000 to about 200,000, or in the range of from 55,000 to about 160,000. Additionally, the cellulose suitable for use in the present invention can be in the form of a sheet, a hammer milled sheet, fiber, or powder. In one embodiment, the cellulose can be a powder having an average particle size of less than about 500 micrometers (“μm”), less than about 400 μm, or less than 300 μm.

The ionic liquid fed to dissolution zone 20 via line 64 can be any ionic liquid capable of at least partially dissolving cellulose. As used herein, the term “ionic liquid” shall denote any substance containing substantially only ions, and which has a melting point at a temperature of 200° C. or less. In one embodiment, the ionic liquid suitable for use in the present invention can be a cellulose dissolving ionic liquid. As used herein, the term “cellulose dissolving ionic liquid” shall denote any ionic liquid capable of dissolving cellulose in an amount sufficient to create an at least 0.1 weight percent cellulose solution. In one embodiment, the ionic liquid fed to dissolution zone 20 via line 64 can have a temperature at least 10° C. above the melting point of the ionic liquid. In another embodiment, the ionic liquid can have a temperature in the range of from about 0 to about 100° C., in the range of from about 20 to about 80° C., or in the range of from 25 to 50° C.

In one embodiment, the ionic liquid fed to dissolution zone 20 via line 64 can comprise water, nitrogen-containing bases, alcohol, or carboxylic acid. The ionic liquid in line 64 can comprise less than about 15 weight percent of each of water, nitrogen-containing bases, alcohol, and carboxylic acid; less than about 5 weight percent of each of water, nitrogen-containing bases, alcohol, and carboxylic acid; or less than 2 weight percent of each of water, nitrogen-containing bases, alcohol, and carboxylic acid.

As mentioned above, an ionic liquid comprises ions. These ions include both cations (i.e., positively charged ions) and anions (i.e., negatively charged ions). In one embodiment, the cations of the ionic liquid suitable for use in the present invention can include, but are not limited to, imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations, which correspond to the following structures:

In the above structures, R₁ and R₂ can independently be a C₁ to C₈ alkyl group, a C₂ to C₈ alkenyl group, or a C₁ to C₈ alkoxyalkyl group. R₃, R₄, and R₅ can independently be a hydrido, a C₁ to C₈ alkyl group, a C₂ to C₈ alkenyl group, a C₁ to C₈ alkoxyalkyl group, or a C₁ to C₈ alkoxy group. In one embodiment, the cation of the ionic liquid used in the present invention can comprise an alkyl substituted imidazolium cation, where R₁ is a C₁ to C₄ alkyl group, and R₂ is a different C₁ to C₄ alkyl group.

In one embodiment of the present invention, the cellulose dissolving ionic liquid can be a carboxylated ionic liquid. As used herein, the term “carboxylated ionic liquid” shall denote any ionic liquid comprising one or more carboxylate anions. Carboxylate anions suitable for use in the carboxylated ionic liquids of the present invention include, but are not limited to, C₁ to C₂₀ straight- or branched-chain carboxylate or substituted carboxylate anions. Examples of suitable carboxylate anions for use in the carboxylated ionic liquid include, but are not limited to, formate, acetate, propionate, butyrate, valerate, hexanoate, lactate, oxalate, or chloro-, bromo-, fluoro-substituted acetate, propionate, or butyrate and the like. In one embodiment, the anion of the carboxylated ionic liquid can be a C₂ to C₆ straight-chain carboxylate. Furthermore, the anion can be acetate, propionate, butyrate, or a mixture of acetate, propionate, and/or butyrate.

Examples of carboxylated ionic liquids suitable for use in the present invention include, but are not limited to, 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium propionate, 1-ethyl-3-methylimidazolium butyrate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium propionate, 1-butyl-3-methylimidazolium butyrate, or mixtures thereof.

In one embodiment of the present invention, the carboxylated ionic liquid can contain sulfur in an amount less than 200 parts per million by weight (“ppmw”), less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw based on the total ion content of the carboxylated ionic liquid. Additionally, the carboxylated ionic liquid can contain a total halide content of less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw based on the total ion content of the carboxylated ionic liquid. Furthermore, the carboxylated ionic liquid can contain a total metal content of less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw based on the total ion content of the carboxylated ionic liquid. In one embodiment, carboxylated ionic liquid can contain transition metals in an amount less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw. Sulfur, halide, and metal content of the carboxylated ionic liquid can be determined by x-ray fluorescence (“XRF”) spectroscopy.

The carboxylated ionic liquid of the present invention can be formed by any process known in the art for making ionic liquids having at least one carboxylate anion. In one embodiment, the carboxylated ionic liquid of the present invention can be formed by first forming an intermediate ionic liquid. The intermediate ionic liquid can be any known ionic liquid that can participate in an anion exchange reaction.

In one embodiment, the intermediate ionic liquid can comprise a plurality of cations such as, for example, imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations, which correspond to the following structures:

In the above structures, R₁ and R₂ can independently be a C₁ to C₈ alkyl group, a C₂ to C₈ alkenyl group, or a C₁ to C₈ alkoxyalkyl group. R₃, R₄, and R₅ can independently be a hydrido, a C₁ to C₈ alkyl group, a C₂ to C₈ alkenyl group, a C₁ to C₈ alkoxyalkyl group, or a C₁ to C₈ alkoxy group. In one embodiment, the cation of the intermediate ionic liquid used in the present invention can comprise an alkyl substituted imidazolium cation, where R₁ is a C₁ to C₄ alkyl group, and R₂ is a different C₁ to C₄ alkyl group. In one embodiment, the cation of the intermediate ionic liquid can comprise 1-ethyl-3-methylimidazolium or 1-butyl-3-methylimidazolium.

Additionally, the intermediate ionic liquid can comprise a plurality of anions. In one embodiment, the intermediate ionic liquid can comprise a plurality of carboxylate anions, such as, for example, formate, acetate, and/or propionate anions.

In one embodiment, the intermediate ionic liquid can comprise an alkyl amine formate. The amine cation of the alkyl amine formate can comprise any of the above-described substituted or unsubstituted imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations. In one embodiment, the amine of the alkyl amine formate can be an alkyl substituted imidazolium, alkyl substituted pyrazolium, alkyl substituted oxazolium, alkyl substituted triazolium, alkyl substituted thiazolium, and mixtures thereof. In one embodiment, the amine of the alkyl amine formate can be an alkyl substituted imidazolium. Examples of alkyl amine formates suitable for use in the present invention include, but are not limited to, 1-methyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium formate, 1-propyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium formate, 1-pentyl-3-methylimidazolium formate, and/or 1-octyl-3-methylimidazolium formate.

The intermediate ionic liquid useful in the present invention can be formed by contacting at least one amine with at least one alkyl formate. Amines suitable for use in the present invention include, but are not limited to, substituted or unsubstituted imidazoles, pyrazoles, oxazoles, triazoles, and/or thiazoles. In one embodiment, the alkyl amine formate can be formed by contacting at least one alkyl substituted imidazole with at least one alkyl formate. Examples of alkyl substituted imidazoles suitable for use in forming the intermediate ionic liquid include, but are not limited to, 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, 1-butylimidazole, 1-hexylimidazole, and/or 1-octylimidazole. Examples of alkyl formates suitable for use in forming the intermediate ionic liquid include, but are not limited to, methyl formate, ethyl formate, propyl formate, isopropyl formate, butyl formate, isobutyl formate, tert-butyl formate, hexyl formate, octyl formate, and the like. In one embodiment, the alkyl formate used in forming the intermediate ionic liquid can comprise methyl formate.

Once the intermediate ionic liquid has been formed, the intermediate ionic liquid can be contacted with one or more carboxylate anion donors at a contact time, pressure, and temperature sufficient to cause the at least partial conversion of the intermediate ionic liquid to at least one of the above-mentioned carboxylated ionic liquids. Such interconversion can be accomplished via anion exchange between the carboxylate anion donor and the intermediate ionic liquid. In one embodiment, at least a portion of the formate of the alkyl amine formate can be replaced via anion exchange with a carboxylate anion originating from one or more carboxylate anion donors.

Carboxylate anion donors useful in the present invention can include any substance capable of donating at least one carboxylate anion. Examples of carboxylate anion donors suitable for use in the present invention include, but are not limited to, carboxylic acids, anhydrides, and/or alkyl carboxylates. In one embodiment, the carboxylate anion donor can comprise one or more C₂ to C₂₀ straight- or branched-chain alkyl or aryl carboxylic acids, anhydrides, or methyl esters. Additionally, the carboxylate anion donor can comprise one or more C₂ to C₁₂ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters. Furthermore, the carboxylate anion donor can comprise one or more C₂ to C₄ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters. In one embodiment, the carboxylate anion donor can comprise at least one anhydride, which can comprise acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, hexanoic anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauric anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, substituted benzoic anhydrides, phthalic anhydride, isophthalic anhydride, and mixtures thereof.

The amount of carboxylate anion donor useful in the present invention can be any amount suitable to convert at least a portion of the intermediate ionic liquid to a carboxylated ionic liquid. In one embodiment, the carboxylate anion donor can be present in a molar ratio with the intermediate ionic liquid in the range of from about 1:1 to about 20:1 carboxylate anion donor-to-intermediate ionic liquid anion content, or in the range of from 1:1 to 6:1 carboxylate anion donor-to-intermediate ionic liquid anion content. In one embodiment, when alkyl amine formate is present as the intermediate ionic liquids, the carboxylate anion donor can be present in an amount in the range of from 1 to 20 molar equivalents per alkyl amine formate, or in the range of from 1 to 6 molar equivalents per alkyl amine formate.

The anion exchange between the intermediate ionic liquid and the carboxylate anion donor can be accomplished in the presence of at least one alcohol. Alcohols useful in the present invention include, but are not limited to, alkyl or aryl alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenol, and the like. In one embodiment, the alcohol can be methanol. The amount of alcohol present in the contact mixture during interconversion of the intermediate ionic liquid can be in the range of from about 0.01 to about 20 molar equivalents of the ionic liquid, or in the range of from 1 to 10 molar equivalents of the ionic liquid.

In one embodiment, water can be present in the contact mixture during the anion exchange between the intermediate ionic liquid and the carboxylate anion donor. The amount of water present in the contact mixture during interconversion of the intermediate ionic liquid can be in the range of from about 0.01 to about 20 molar equivalents of the ionic liquid, or in the range of from 1 to 10 molar equivalents of the ionic liquid.

As mentioned above, the interconversion of the intermediate ionic liquid to the carboxylated ionic liquid can be performed at a contact time, pressure, and temperature sufficient to cause the at least partial conversion of the intermediate ionic liquid to the carboxylated ionic liquid. In one embodiment, the interconversion can be performed for a time in the range of from about 1 minute to about 24 hours, or in the range of from 30 minutes to 18 hours. Additionally, the interconversion can be performed at a pressure up to 21,000 kPa, or up to 10,000 kPa. In one embodiment, the interconversion can be performed at a pressure in the range of from about 100 to about 21,000 kPa, or in the range of from 100 to 10,000 kPa. Furthermore, the interconversion can be performed at a temperature in the range of from about 0 to about 200° C., or in the range of from 25 to 170° C.

In one embodiment, the resulting carboxylated ionic liquid can comprise carboxylate anions comprising substituted or non-substituted C₁ to C₂₀ straight- or branched-chain carboxylate anions. In one embodiment, the carboxylate anion can comprise a C₂ to C₆ straight-chain carboxylate anion. Additionally, the carboxylated ionic liquid can comprise carboxylate anions such as, for example, formate, acetate, propionate, butyrate, valerate, hexanoate, lactate, and/or oxalate. In one embodiment, the carboxylated ionic liquid can comprise at least 50 percent carboxylate anions, at least 70 percent carboxylate anions, or at least 90 percent carboxylate anions. In another embodiment, the carboxylated ionic liquid can comprise at least 50 percent acetate anions, at least 70 percent acetate anions, or at least 90 percent acetate anions.

In an alternative embodiment of the present invention, the above-mentioned cellulose dissolving ionic liquid can be a halide ionic liquid. As used herein, the term “halide ionic liquid” shall denote any ionic liquid that contains at least one halide anion. In one embodiment, the halide anion of the halide ionic liquid can be fluoride, chloride, bromide, and/or iodide. In another embodiment, the halide anion can be chloride and/or bromide. Additionally, as mentioned above, the cation of the cellulose dissolving ionic liquid can comprise, but is not limited to, imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations. Any method known in the art suitable for making a halide ionic liquid can be employed in the present invention.

Examples of halide ionic liquids suitable for use in the present invention include, but are not limited to, 1-butyl-3-methylimidazolium chloride, 1-propyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, or mixtures thereof.

Referring again to FIG. 1, the weight percent of the amount of cellulose fed to dissolution zone 20 to the cumulative amount of ionic liquid (including recycled ionic liquid) fed to dissolution zone 20 can be in the range of from about 1 to about 40 weight percent, in the range of from about 5 to about 25 weight percent, or in the range of from 10 to 20 weight percent based on the combined weight of cellulose and ionic liquid. In one embodiment, the resulting medium formed in dissolution zone 20 can comprise other components, such as, for example, water, alcohol, acylating reagent, and/or carboxylic acids. In one embodiment, the medium formed in dissolution zone 20 can comprise water in an amount in the range of from about 0.001 to about 200 weight percent, in the range of from about 1 to about 100 weight percent, or in the range of from 5 to 15 weight percent based on the entire weight of the medium. Additionally, the medium formed in dissolution zone 20 can comprise a combined concentration of alcohol in an amount in the range of from about 0.001 to about 200 weight percent, in the range of from about 1 to about 100 weight percent, or in the range of from 5 to 15 weight percent based on the entire weight of the medium.

The medium formed in dissolution zone 20 can optionally comprise one or more carboxylic acids. The medium formed in dissolution zone 20 can comprise a total concentration of carboxylic acids in the range of from about 0.01 to about 25 weight percent, in the range of from about 0.05 to about 15 weight percent, or in the range of from 0.1 to 5 weight percent based on the total concentration of ionic liquid in the medium formed in dissolution zone 20. Examples of suitable carboxylic acids useful in this embodiment include, but are not limited to, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid, substituted benzoic acids, phthalic acid, and isophthalic acid. In one embodiment, the carboxylic acid in the medium formed in dissolution zone 20 can comprise acetic acid, propionic acid, and/or butyric acid.

As is described in more detail below with reference to FIG. 2, at least a portion of the carboxylic acids present in the medium formed in dissolution zone 20 can originate from a recycled carboxylated ionic liquid introduced via line 70. Though not wishing to be bound by theory, the inventors have unexpectedly found that the use of carboxylic acid in the medium formed in dissolution zone 20 can reduce the viscosity of the cellulose/ionic liquid solution, thereby enabling easier processing of the solution. Additionally, the presence of carboxylic acid in the medium in dissolution zone 20 appears to reduce the melting points of the ionic liquids employed, thereby allowing processing of the ionic liquids at lower temperatures than predicted.

The medium formed in dissolution zone 20 can optionally comprise an acylating reagent, as is discussed in more detail below. The optional acylating reagent can be introduced into dissolution zone 20 via line 78. In one embodiment, the medium formed in dissolution zone 20 can comprise acylating reagent in an amount in the range of from about 0.01 molar equivalents to about 20 molar equivalents, in the range of from about 0.5 molar equivalents to about 10 molar equivalents, or in the range of from 1.8 molar equivalents to about 4 molar equivalents based on the total amount of cellulose in the medium in dissolution zone 20.

The medium formed in dissolution zone 20 can also comprise recycled ionic liquid, as is discussed in more detail below with reference to FIG. 2. The recycled ionic liquid can be introduced into dissolution zone 20 via line 70. The medium formed in dissolution zone 20 can comprise recycled ionic liquid in an amount in the range of from about 0.01 to about 99.99 weight percent, in the range of from about 10 to about 99 weight percent, or in the range of from 90 to 98 weight percent based on the total amount of ionic liquid in dissolution zone 20.

In one embodiment, the medium can optionally comprise immiscible or substantially immiscible co-solvents. Such co-solvents can comprise one or more co-solvents that are immiscible or sparingly soluble with the cellulose-ionic liquid mixture. Surprisingly, the addition of an immiscible or sparingly soluble co-solvent does not cause precipitation of the cellulose upon contacting the cellulose-ionic liquid mixture. However, upon contact with an acylating reagent, as will be discussed in more detail below, the cellulose can be esterified which can change the solubility of the now cellulose ester-ionic liquid solution with respect to the formerly immiscible or sparingly soluble co-solvent. Accordingly, subsequent to esterification, the contact mixture can become a single phase or highly dispersed mixture of cellulose ester-ionic liquid in the co-solvent. The resulting single phase or dispersed phase has much lower solution viscosity than the initial cellulose-ionic liquid solution.

This discovery is significant in that heretofore highly viscous cellulose solutions can now be used to make cellulose esters while still maintaining the ability to mix and process the solution. The discovery also provides a viable method to process highly viscous cellulose-ionic liquid solutions at lower contact temperatures.

Immiscible or sparingly soluble co-solvents suitable for use in the present invention can comprise alkyl or aryl esters, ketones, alkyl halides, hydrophobic ionic liquids, and the like. Specific examples of immiscible or sparingly soluble co-solvents include, but are not limited to, methyl acetate, ethyl acetate, isopropyl acetate, methyl propionate, methyl butyrate, acetone, methyl ethyl ketone, chloroform, methylene chloride, alkyl immidazolium hexafluorophosphate, alkyl immidazolium triflimide, and the like. In one embodiment, the immiscible or sparingly soluble co-solvents can comprise methyl acetate, methyl propionate, methyl butyrate, methyl ethyl ketone, and/or methylene chloride. The weight ratio of immiscible or sparingly soluble co-solvents to cellulose-ionic liquid mixture can be in the range of from about 1:20 to about 20:1. or in the range of from 1:5 to 5:1.

In one embodiment, the cellulose entering dissolution zone 20 via line 62 can initially be dispersed in the ionic liquid. Dispersion of the cellulose in the ionic liquid can be achieved by any mixing means known in the art. In one embodiment, dispersion of the cellulose can be achieved by mechanical mixing, such as mixing by one or more mechanical homogenizers.

After the cellulose has been dispersed in the ionic liquid, dissolution of the cellulose in dissolution zone 20, along with removal of at least a portion of any volatile components in the mixture, can be achieved using any method known in the art. For example, dissolution of the cellulose can be achieved by lowering the pressure and/or raising the temperature of the cellulose/ionic liquid dispersion initially formed in dissolution zone 20. Accordingly, after the cellulose is dispersed in the ionic liquid, the pressure can be lowered in dissolution zone 20. In one embodiment, the pressure in dissolution zone 20 can be lowered to less than about 100 millimeters mercury (“mm Hg”), or less than 50 mm Hg. Additionally, the cellulose/ionic liquid dispersion can be heated to a temperature in the range of from about 60 to about 100° C., or in the range of from 70 to about 85° C. After dissolution, the resulting solution can be maintained at the above-described temperatures and pressures for a time in the range of from about 0 to about 100 hours, or in the range of from about 1 to about 4 hours. The cellulose solution formed in dissolution zone 20 can comprise cellulose in an amount in the range of from about 1 to about 40 weight percent, or in the range of from 5 to 20 weight percent, based on the entire weight of the solution. In another embodiment, the cellulose solution formed in dissolution zone 20 can comprise dissolved cellulose in an amount of at least 10 weight percent based on the entire weight of the solution.

After dissolution, at least a portion of the resulting cellulose solution can be removed from dissolution zone 20 via line 66 and routed to esterification zone 40. In one embodiment, at least one acylating reagent can be introduced into esterification zone 40 to esterify at least a portion of the cellulose. As mentioned above, in another embodiment, at least one acylating reagent can be introduced into dissolution zone 20. Additionally, the acylating reagent can be added after the cellulose has been dissolved in the ionic liquid. Optionally, at least a portion of the acylating reagent can be added to the ionic liquids prior to dissolution of the cellulose in the ionic liquid. Regardless of where the acylating reagent is added, at least a portion of the cellulose in esterification zone 40 can undergo esterification subsequent to being contacted with the acylating reagent.

As used herein, the term “acylating reagent” shall denote any chemical compound capable of donating at least one acyl group to a cellulose. As used herein, the term “acyl group” shall denote any organic radical derived from an organic acid by the removal of a hydroxyl group. Acylating reagents useful in the present invention can be one or more C₁ to C₂₀ straight- or branched-chain alkyl or aryl carboxylic anhydrides, carboxylic acid halides, diketene, or acetoacetic acid esters. Examples of carboxylic anhydrides suitable for use as acylating reagents in the present invention include, but are not limited to, acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, hexanoic anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauric anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, substituted benzoic anhydrides, phthalic anhydride, and isophthalic anhydride. Examples of carboxylic acid halides suitable for use as acylating reagents in the present invention include, but are not limited to, acetyl, propionyl, butyryl, hexanoyl, 2-ethylhexanoyl, lauroyl, palmitoyl, and stearoyl chlorides. Examples of acetoacetic acid esters suitable for use as acylating reagents in the present invention include, but are not limited to, methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate, and tert-butyl acetoacetate. In one embodiment, the acylating reagents can be C₂ to C₉ straight- or branched-chain alkyl carboxylic anhydrides selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, 2-ethylhexanoic anhydride, and nonanoic anhydride.

The reaction medium formed in esterification zone 40 can comprise cellulose in an amount in the range of from about 1 to about 40 weight percent, in the range of from about 5 to about 25 weight percent, or in the range of from 10 to 20 weight percent, based on the weight of the ionic liquid in the reaction medium. Additionally, the reaction medium formed in esterification zone 40 can comprise ionic liquid in an amount in the range of from about 20 to about 98 weight percent, in the range of from about 30 to about 95 weight percent, or in the range of from 50 to 90 weight percent based on the total weight of the reaction medium. Furthermore, the reaction medium formed in esterification zone 40 can comprise acylating reagent in an amount in the range of from about 1 to about 50 weight percent, in the range of from about 5 to about 30 weight percent, or in the range of from 10 to 20 weight percent based on the total weight of the reaction medium. Furthermore, the reaction medium formed in esterification zone 40 can have a cumulative concentration of nitrogen containing bases and carboxylic acids in an amount less than 15 weight percent, less than 5 weight percent, or less than 2 weight percent.

In one embodiment, the weight ratio of cellulose-to-acylating reagent in esterification zone 40 can be in the range of from about 90:10 to about 10:90, in the range of from about 60:40 to about 25:75, or in the range of from 45:55 to 35:65. In one embodiment, the acylating reagent can be present in esterification zone 40 in an amount less than 5, less than 4, less than 3, or less than 2.7 molar equivalents per anhydroglucose unit.

In one embodiment of the present invention, when a halide ionic liquid is employed as the cellulose dissolving ionic liquid, a limited excess of acylating reagent can be employed in the esterification of the cellulose to achieve a cellulose ester with a particular DS. Thus, in one embodiment, less than 20 percent molar excess, less than 10 percent molar excess, less than 5 percent molar excess, or less than 1 percent excess of acylating reagent can be employed during esterification.

Optionally, one or more catalysts can be introduced into esterification zone 40 to aid in esterification of the cellulose. The catalyst employed in the present invention can be any catalyst that increases the rate of esterification in esterification zone 40. Examples of catalysts suitable for use in the present invention include, but are not limited to, protic acids of the type sulfuric acid, alkyl sulfonic acids, aryl sulfonic acids, functional ionic liquids, and weak Lewis acids of the type MXn, where M is a transition metal exemplified by B, Al, Fe, Ga, Sb, Sn, As, Zn, Mg, or Hg, and X is halogen, carboxylate, sulfonate, alkoxide, alkyl, or aryl. In one embodiment, the catalyst is a protic acid. The protic acid catalysts can have a pKa in the range of from about −5 to about 10, or in the range of from −2.5 to 2.0. Examples of suitable protic acid catalysts include methane sulfonic acid (“MSA”), p-toluene sulfonic acid, and the like. In one embodiment, the one or more catalysts can be Lewis acids. Examples of Lewis acids suitable for use as catalysts include ZnCl2, Zn(OAc)2, and the like. When a catalyst is employed, the catalyst can be added to the cellulose solution prior to adding the acylating reagent. In another embodiment the catalyst can be added to the cellulose solution as a mixture with the acylating reagent.

Additionally, functional ionic liquids can be employed as catalysts during esterification of the cellulose. Functional ionic liquids are ionic liquids containing specific functional groups, such as hydrogen sulfonate, alkyl or aryl sulfonates, and carboxylates, that effectively catalyze the esterification of cellulose by the acylating reagent. Examples of functional ionic liquids include 1-alkyl-3-methylimidazolium hydrogen sulfate, methyl sulfonate, tosylate, and trifluoroacetate, where the alkyl can be a C₁ to C₁₀ straight-chain alkyl group. Additionally, suitable functional ionic liquids for use in the present invention are those in which the functional group is covalently linked to the cation. Thus, functional ionic liquids can be ionic liquids containing functional groups, and are capable of catalyzing the esterification of cellulose with an acylating reagent.

An example of a covalently-linked functional ionic liquid suitable for use in the present invention includes, but is not limited to, the following structure:

where at least one of the R₁, R₂, R₃, R₄, R₅ groups are replaced with the group (CHX)_(n)Y, where X is hydrogen or halide, n is an integer in the range of from 1 to 10, and Y is sulfonic or carboxylate and the remainder R₁, R₂, R₃, R₄, R₅ groups are those previously described in relation to the cations suitable for use as the cellulose dissolving ionic liquid. Examples of cations suitable for use in the functional ionic liquids to be used in the present invention include, but are not limited to, 1-alkyl-3-(1-carboxy-2,2-difluoroethyl)imidazolium, 1-alkyl-3-(1-carboxy-2,2-difluoropropyl)imidazolium, 1-alkyl-3-(1-carboxy-2,2-difluoro-butyl)imidazolium, 1-alkyl-3-(1-carboxy-2,2-difluorohexyl)imidazolium, 1-alkyl-3-(1-sulfonylethyl)imidazolium, 1-alkyl-3-(1-sulfonylpropyl)imidazolium, 1-alkyl-3-(1-sulfonylbutyl)imidazolium, and 1-alkyl-3-(1-sulfonylhexyl)imidazolium, where the alkyl can be a C₁ to C₁₀ straight-chain alkyl group.

The amount of catalyst used to catalyze the esterification of cellulose may vary depending upon the type of catalyst employed, the type of acylating reagent employed, the type of ionic liquid, the contact temperature, and the contact time. Thus, a broad concentration of catalyst employed is contemplated by the present invention. In one embodiment, the amount of catalyst employed in esterification zone 40 can be in the range of from about 0.01 to about 30 mol percent catalyst per anhydroglucose unit (“AGU”), in the range of from about 0.05 to about 10 mol percent catalyst per AGU, or in the range of from 0.1 to 5 mol percent catalyst per AGU. In one embodiment, the amount of catalyst employed can be less than 30 mol percent catalyst per AGU, less than 10 mol percent catalyst per AGU, less than 5 mol percent catalyst per AGU, or less than 1 mol percent catalyst per AGU. In another embodiment, when a catalyst is employed as a binary component, the amount of binary component employed can be in the range of from about 0.01 to about 100 mol percent per AGU, in the range of from about 0.05 to about 20 mol percent per AGU, or in the range of from 0.1 to 5 mol percent per AGU.

The inventors have discovered a number of surprising and unpredictable advantages apparently associated with employing a catalyst as a binary component during the esterification of cellulose. For example, the inventors have discovered that the inclusion of a binary component can accelerate the rate of esterification. Very surprisingly, the binary component can also serve to improve solution and product color, prevent gellation of the esterification mixture, provide increased DS values in relation to the amount of acylating reagent employed, and/or help to decrease the molecular weight of the cellulose ester product. Though not wishing to be bound by theory, it is believed that the use of a binary component acts to change the network structure of the ionic liquid containing the dissolved cellulose ester. This change in network structure may lead to the observed surprising and unpredicted advantages of using the binary component.

As mentioned above, at least a portion of the cellulose can undergo an esterification reaction in esterification zone 40. The esterification reaction carried out in esterification zone 40 can operate to convert at least a portion of the hydroxyl groups contained on the cellulose to ester groups, thereby forming a cellulose ester. As used herein, the term “cellulose ester”

shall denote a cellulose polymer having at least one ester substituent. In one embodiment, at least a portion of the ester groups on the resulting cellulose ester can originate from the above-described acylating reagent. The cellulose esters thus prepared can comprise the following structure:

where R₂, R₃, and R₆ can independently be hydrogen, so long as R₂, R₃, and R₆ are not all hydrogen simultaneously, or a C₁ to C₂₀ straight- or branched-chain alkyl or aryl groups bound to the cellulose via an ester linkage.

In one embodiment, when the ionic liquid employed is a carboxylated ionic liquid, one or more of the ester groups on the resulting cellulose ester can originate from the ionic liquid in which the cellulose is dissolved. The amount of ester groups on the resulting cellulose ester that originate from the carboxylated ionic liquid can be at least 10 percent, at least 25 percent, at least 50 percent, or at least 75 percent.

Additionally, the ester group on the cellulose ester originating from the carboxylated ionic liquid can be a different ester group than the ester group on the cellulose ester that originates from the acylating reagent. Though not wishing to be bound by theory, it is believed that when an acylating reagent is introduced into a carboxylated ionic liquid, an anion exchange can occur such that a carboxylate ion originating from the acylating reagent replaces at least a portion of the carboxylate anions in the carboxylated ionic liquid, thereby creating a substituted ionic liquid. When the carboxylate ion originating from the acylating reagent is of a different type than the carboxylate anions of the ionic liquid, then the substituted ionic liquid can comprise at least two different types of carboxylate anions. Thus, so long as the carboxylate anion from the carboxylated ionic liquid comprises a different acyl group than is found on the acylating reagent, at least two different acyl groups are available for esterification of the cellulose. By way of illustration, if cellulose was dissolved in 1-butyl-3-methylimidazolium acetate (“[BMIm]OAc” or “[BMIm]acetate”) and a propionic anhydride (“Pr₂O”) acylating reagent were added to the carboxylated ionic liquid, the carboxylated ionic liquid can become a substituted ionic liquid, comprising a mixture of [BMIm]acetate and [BMIm]propionate. Thus, the process of forming a cellulose ester via this process can be illustrated as follows:

As illustrated, contacting a solution of cellulose dissolved in [BMIm]acetate with a propionic anhydride can result in the formation of a cellulose ester comprising both acetate ester substituents and propionate ester substituents. Thus, at least a portion of the ester groups on the cellulose ester can originate from the ionic liquid, and at least a portion of the ester groups can originate from the acylating reagent. Additionally, at least one of the ester groups donated by the ionic liquid can be an acyl group. In one embodiment, all of the ester groups donated by the ionic liquid can be acyl groups.

Therefore, in one embodiment, the cellulose ester prepared by methods of the present invention can be a mixed cellulose ester. As used herein, the term “mixed cellulose ester” shall denote a cellulose ester having at least two different ester substituents on a single cellulose ester polymer chain. The mixed cellulose ester of the present invention can comprise a plurality of first pendant acyl groups and a plurality of second acyl groups, where the first pendant acyl groups originate from the ionic liquid, and the second pendant acyl groups originate from the acylating reagent. In one embodiment, the mixed cellulose ester can comprise a molar ratio of at least two different acyl pendant groups in the range of from about 1:10 to about 10:1, in the range of from about 2:8 to about 8:2, or in the range of from 3:7 to 7:3. Additionally, the first and second pendant acyl groups can comprise acetyl, propionyl, and/or butyryl groups.

In one embodiment, at least one of the first pendant acyl groups can be donated by the ionic liquid or at least one of the second pendant acyl groups can be donated by the ionic liquid. As used herein, the term “donated,” with respect to esterification, shall denote a direct transfer of an acyl group. Comparatively, the term “originated,” with respect to esterification, can signify either a direct transfer or an indirect transfer of an acyl group. In one embodiment of the invention, at least 50 percent of the above-mentioned first pendant acyl groups can be donated by the ionic liquid, or at least 50 percent of the second pendant acyl groups can be donated by the ionic liquid. Furthermore, at least 10 percent, at least 25 percent, at least 50 percent, or at least 75 percent of all of the pendant acyl groups on the resulting cellulose ester can result from donation of an acyl group by the ionic liquid.

In one embodiment, the above-described mixed cellulose ester can be formed by a process where a first portion of the first pendant acyl groups can initially be donated from the acylating reagent to the carboxylated ionic liquid, and then the same acyl groups can be donated from the carboxylated ionic liquid to the cellulose (i.e., indirectly transferred from the acylating reagent to the cellulose, via the ionic liquid). Additionally, a second portion of the first pendant acyl groups can be donated directly from the acylating reagent to the cellulose.

Referring still to FIG. 1, the temperature in esterification zone 40 during the above-described esterification process can be in the range of from about 0 to about 120° C., in the range of from about 20 to about 80° C., or in the range of from 25 to 50° C. Additionally, the cellulose can have a residence time in esterification zone 40 in the range of from about 1 minute to about 48 hours, in the range of from about 30 minutes to about 24 hours, or in the range of from 1 to 5 hours.

Subsequent to the above-described esterification process, an esterified medium can be withdrawn from esterification zone 40 via line 80. The esterified medium withdrawn from esterification zone 40 can comprise an initial cellulose ester. The initial cellulose ester in line 80 can be a non-random cellulose ester. As used herein, the term “non-random cellulose ester” shall denote a cellulose ester having a non-Gaussian distribution of substituted monomers as determined by NMR spectroscopy. Additionally, as mentioned above, the initial cellulose ester in line 80 can be a mixed cellulose ester.

The initial cellulose ester can have a degree of substitution (“DS”) in the range of from about 0.1 to about 3.0, in the range of from about 1.8 to about 2.9, or in the range of from 2.0 to 2.6. In another embodiment, the initial cellulose ester can have a DS of at least 2. Additionally, the initial cellulose ester can have a DS of less than 3.0, or less than 2.9.

Furthermore, the degree of polymerization (“DP”) of the cellulose esters prepared by the methods of the present invention can be at least 10, at least 50, at least 100, or at least 250. In another embodiment, the DP of the initial cellulose ester can be in the range of from about 5 to about 1,000, or in the range of from 10 to 250.

The esterified medium in line 80 can comprise the initial cellulose ester in an amount in the range of from about 2 to about 80 weight percent, in the range of from about 10 to about 60 weight percent, or in the range of from 20 to 40 weight percent based on weight of ionic liquid. In addition to the initial cellulose ester, the esterified medium withdrawn from esterification zone 40 via line 80 can also comprise other components, such as, for example, altered ionic liquid, residual acylating reagent, and/or one or more carboxylic acids. In one embodiment, the esterified medium in line 80 can comprise a ratio of altered ionic liquid to initial ionic liquid introduced into dissolution zone 20 in an amount in the range of from about 0.01 to about 99.99 weight percent, in the range of from about 10 to about 99 weight percent, or in the range of from 90 to 98 weight percent based on the total amount of initial ionic liquid. Additionally, the esterified medium in line 80 can comprise residual acylating reagent in an amount less than about 20 weight percent, less than about 10 weight percent, or less than 5 weight percent.

Furthermore, the esterified medium in line 80 can comprise a total concentration of carboxylic acids in an amount in the range of from about 0.01 to about 40 weight percent, in the range of from about 0.05 to about 20 weight percent, or in the range of from 0.1 to 5 weight percent. In another embodiment, the esterified medium in line 80 can comprise a total concentration of carboxylic acids in an amount less than 40, less than 20, or less than 5 weight percent. Carboxylic acids that can be present in the esterified medium in line 80 include, but are not limited to, formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid, substituted benzoic acids, phthalic acid, and/or isophthalic acid.

The esterified medium in line 80 can be routed to cellulose ester recovery/treatment zone 50. As is discussed in more detail below with reference to FIG. 2, at least a portion of the cellulose ester can optionally be subjected to at least one randomization process in recovery/treatment zone 50, thereby producing a randomized cellulose ester. Additionally, as is discussed in more detail below with reference to FIG. 2, at least a portion of the cellulose ester can be caused to precipitate out of the esterified medium, at least a portion of which can thereafter be separated from the resulting mother liquor.

Referring still to FIG. 1, at least a portion of the cellulose ester precipitated and recovered in recovery/treatment zone 50 can be withdrawn via line 90 as a final cellulose ester. The final cellulose ester exiting recovery/treatment zone 50 via line 90 can have a number average molecular weight (“Mn”) in the range of from about 1,200 to about 200,000, in the range of from about 6,000 to about 100,000, or in the range of from 10,000 to 75,000. Additionally, the final cellulose ester exiting recovery/treatment zone 50 via line 90 can have a weight average molecular weight (“Mw”) in the range of from about 2,500 to about 420,000, in the range of from about 10,000 to about 200,000, or in the range of from 20,000 to 150,000. Furthermore, the final cellulose ester exiting recovery/treatment zone 50 via line 90 can have a Z average molecular weight (“Mz”) in the range of from about 4,000 to about 850,000, in the range of from about 12,000 to about 420,000, or in the range of from 40,000 to 330,000. The final cellulose ester exiting recovery/treatment zone 50 via line 90 can have a polydispersity in the range of from about 1.3 to about 7, in the range of from about 1.5 to about 5, or in the range of from 1.8 to 3. Additionally, the final cellulose ester in line 90 can have a DP and DS as described above in relation to the initial cellulose ester in line 80. Furthermore, the cellulose ester can be random or non-random, as is discussed in more detail below with reference to FIG. 2. Moreover, the final cellulose ester in line 90 can comprise a plurality of ester substituents as described above. Also, the final cellulose ester in line 90 can optionally be a mixed cellulose ester as described above.

In one embodiment, the cellulose ester in line 90 can be in the form of a wet cake. The wet cake in line 90 can comprise a total liquid content of less than 99, less than 50, or less than 25 weight percent. Furthermore, the wet cake in line 90 can comprise a total ionic liquid concentration of less than 1, less than 0.01, or less than 0.0001 weight percent. Additionally, the wet cake in line 90 can comprise a total alcohol content of less than 100, less than 50, or less than 25 weight percent. Optionally, as is discussed in greater detail below with reference to FIG. 2, the final cellulose ester can be dried to produce a dry final cellulose ester product.

The cellulose esters prepared by the methods of this invention can be used in a variety of applications. Those skilled in the art will understand that the specific application will depend upon various characteristics of the cellulose ester, such as, for example, the type of acyl substituent, DS, molecular weight, and type of cellulose ester copolymer. In one embodiment of the invention, the cellulose esters can be used in thermoplastic applications in which the cellulose ester is used to make film or molded objects. Examples of cellulose esters suitable for use in thermoplastic applications include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, or mixtures thereof. In yet another embodiment of the invention, the cellulose esters can be used in coating applications. Examples of coating applications include but, are not limited to, automotive, wood, plastic, or metal coating processes. Examples of cellulose esters suitable for use in coating applications include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, or mixtures thereof.

In still another embodiment of the invention, the cellulose esters can be used in personal care applications. In personal care applications, cellulose esters can be dissolved or suspended in appropriate solvents. The cellulose ester can then act as a structuring agent, delivery agent, and/or film forming agent when applied to skin or hair. Examples of cellulose esters suitable for use in personal care applications include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose hexanoate, cellulose 2-ethylhexanoate, cellulose laurate, cellulose palmitate, cellulose stearate, or mixtures thereof.

In still another embodiment of the invention, the cellulose esters can be used in drug delivery applications. In drug delivery applications, the cellulose ester can act as a film former such as in the coating of tablets or particles. The cellulose ester can also be used to form amorphous mixtures of poorly soluble drugs, thereby improving the solubility and bioavailability of the drugs. The cellulose esters can also be used in controlled drug delivery, where the drug can be released from the cellulose ester matrix in response to external stimuli such as a change in pH. Examples of preferred cellulose esters suitable for use in drug delivery applications include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, or mixtures thereof.

In still another embodiment of the invention, the cellulose esters of the present invention can be used in applications involving solvent casting of film. Examples of such applications include photographic film and protective film for liquid crystalline displays. Examples of cellulose esters suitable for use in solvent cast film applications include cellulose triacetate, cellulose acetate, cellulose propionate, and cellulose acetate propionate.

Referring still to FIG. 1, at least a portion of the mother liquor produced in cellulose ester recovery/treatment zone 50 can be withdrawn via line 86 and routed to ionic liquid recovery/treatment zone 60. As will be discussed in further detail below with reference to FIG. 2, the mother liquor can undergo various treatments in ionic liquid recovery/treatment zone 60. Such treatment can include, but is not limited to, volatiles removal and reformation of the ionic liquid. Reformation of the ionic liquid can include, but is not limited to, (1) anion homogenization, and (2) anion exchange. Accordingly, a recycled ionic liquid can be formed in ionic liquid recovery/treatment zone 60.

In one embodiment, at least a portion of the recycled ionic liquid can be withdrawn from ionic liquid recovery/treatment zone 60 via line 70. The recycled ionic liquid in line 70 can have a composition such as described above in relation to the ionic liquid in line 64 of FIG. 1. The production and composition of the recycled ionic liquid will be discussed in greater detail below with reference to FIG. 2. As mentioned above, at least a portion of the recycled ionic liquid in line 70 can be routed back to dissolution zone 20. In one embodiment, at least about 80 weight percent, at least about 90 weight percent, or at least 95 weight percent of the recycled ionic liquid produced in ionic liquid recovery/treatment zone 60 can be routed to dissolution zone 20.

Referring now to FIG. 2, a more detailed diagram for the production of cellulose esters is depicted, including optional steps for improving the overall efficacy and/or efficiency of the esterification process. In the embodiment depicted in FIG. 2, a cellulose can be introduced into an optional modification zone 110 via line 162. The cellulose fed to optional modification zone 110 can be substantially the same as the cellulose in line 62 described above with reference to FIG. 1. In optional modification zone 110, the cellulose can be modified employing at least one modifying agent.

As mentioned above, water may be employed as the modifying agent. Thus, in one embodiment of the present invention, a water-wet cellulose can be withdrawn from optional modification zone 110 and added to one or more ionic liquids in dissolution zone 120. In one embodiment, the cellulose can be mixed with water then pumped into one or more ionic liquids as a slurry. Alternatively, excess water can be removed from the cellulose, and thereafter the cellulose can be added to the one or more ionic liquids in the form of a wet cake. In this embodiment, the cellulose wet cake can contain associated water in an amount in the range of from about 10 to about 95 weight percent, in the range of from about 20 to about 80 weight percent, or in the range of from 25 to 75 weight percent, based on the combined weight of the cellulose and associated water.

Though not wishing to be bound by theory, the addition of water wet cellulose has unexpectedly and unpredictably been found to provide at least three heretofore unknown benefits. First, water can increase dispersion of the cellulose in the one or more ionic liquids so that when removal of water is initiated while heating the cellulose, the cellulose rapidly dissolves in the one or more ionic liquids. Secondly, water appears to reduce the melting points of ionic liquids that are normally solids at room temperature, thus allowing processing of ionic liquids at ambient temperatures. A third benefit is that the molecular weight of cellulose esters prepared using initially water wet cellulose is reduced during the above-discussed esterification in esterification zone 40 when compared to cellulose esters prepared using initially dry cellulose.

This third benefit is particularly surprising and useful. Under typical cellulose ester processing conditions, the molecular weight of cellulose is not reduced during dissolution or during esterification. That is, the molecular weight of the cellulose ester product is directly proportionate to the molecular weight of the initial cellulose. Typical wood pulps used to prepare cellulose esters generally have a DP in the range of from about 1,000 to about 3,000. However, the desired DP range of cellulose esters can be from about 10 to about 500. Thus, in the absence of molecular weight reduction during esterification, the cellulose must be specially treated prior to dissolving the cellulose in the ionic liquid or after dissolving in the ionic liquid but prior to esterification. However, when employing water as at least one of the optional modifying agents, pretreatment of the cellulose is not required since molecular weight reduction can occur during esterification. Accordingly, in one embodiment of the present invention, the DP of the modified cellulose subjected to esterification can be within about 10 percent of, within about 5 percent of, within 2 percent of, or substantially the same as the DP of the initial cellulose subjected to modification. However, the DP of the cellulose ester produced in accordance with embodiments of the present invention can be less than about 90 percent, less than about 70 percent, or less than 50 percent of the DP of the modified cellulose subjected to esterification.

Referring still to FIG. 2, the optionally modified cellulose in line 166 can be introduced into dissolution zone 120. Once in dissolution zone 120, the optionally modified cellulose can be dispersed in one or more ionic liquids, as described above with reference to dissolution zone 20 in FIG. 1. Subsequently, at least a portion of the modifying agent in the resulting cellulose/ionic liquid mixture can be removed. In one embodiment, at least 50 weight percent of all modifying agents can be removed, at least 75 weight percent of all modifying agents can be removed, at least 95 weight percent of all modifying agents can be removed, or at least 99 weight percent of all modifying agents can be removed from the cellulose/ionic liquid mixture. Removal of one or more modifying agents in dissolution zone 120 can be accomplished by any means known in the art for liquid/liquid separation, such as, for example, distillation, flash vaporization, and the like. Removed modifying agent can be withdrawn from dissolution zone 120 via line 124.

After removal of the modifying agent, dissolution zone 120 can produce a cellulose solution in substantially the same manner as dissolution zone 20, as described above with reference to FIG. 1. Thereafter, a cellulose solution can be withdrawn from dissolution zone 120 via line 176. The cellulose solution in line 176 can comprise ionic liquid, cellulose, and a residual concentration of one or more optional modifying agents. The cellulose solution in line 176 can comprise cellulose in an amount in the range of from about 1 to about 40 weight percent, in the range of from about 5 to about 30 weight percent, or in the range of from 10 to 20 weight percent, based on the weight of the ionic liquid. Furthermore, the cellulose solution in line 176 can comprise a cumulative amount of residual modifying agents in an amount of less than about 50 weight percent, less than about 25 weight percent, less than about 15 weight percent, less than about 5 weight percent, or less than 1 weight percent.

In the embodiment of FIG. 2, at least a portion of the cellulose solution in line 176 can be introduced into esterification zone 140. Esterification zone 140 can be operated in substantially the same manner as esterification zone 40, as described above with reference to FIG. 1. For example, an acylating reagent can be introduced into esterification zone 140 via line 178. As in esterification zone 40, the acylating reagent can esterify at least a portion of the cellulose in esterification zone 140. Additionally, as described above, at least a portion of the resulting cellulose ester can comprise one or more ester substituents that originated from and or were donated by the ionic liquid.

After esterification in esterification zone 140, an esterified medium can be withdrawn via line 180. The esterified medium in line 180 can be substantially the same as the esterified medium in line 80, as described above with reference to FIG. 1. Thus, the esterified medium in line 180 can comprise an initial cellulose ester and other components, such as, for example, altered ionic liquid, residual acylating reagent, one or more carboxylic acids, and/or one or more catalysts. The concentrations of the initial cellulose ester and other components in the esterified medium in line 180 can be substantially the same as the esterified medium in line 80 described above with reference to FIG. 1.

Referring still to FIG. 2, as mentioned above, the initial cellulose ester produced in esterification zone 140 can be a non-random cellulose ester. In one embodiment, at least a portion of the initial cellulose in line 180 can optionally be introduced into randomization zone 151 to undergo randomization, thereby creating a random cellulose ester. Randomization of the initial cellulose can comprise introducing at least one randomizing agent into randomization zone 151 via line 181. Additionally, as will be discussed in further detail below, at least a portion of the randomization agent introduced into randomization zone 151 can be introduced via line 194.

The randomization agent employed in the present invention can be any substance capable lowering the DS of the cellulose ester via hydrolysis or alcoholysis, and/or by causing migration of at least a portion of the acyl groups on the cellulose ester from one hydroxyl to a different hydroxyl, thereby altering the initial monomer distribution. Examples of suitable randomizing agents include, but are not limited to water and/or alcohols. Alcohols suitable for use as the randomizing agent include, but are not limited to methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenol and the like. In one embodiment, methanol can be employed as the randomizing agent introduced via line 181.

The amount of randomizing agent introduced into randomization zone 151 can be in the range of from about 0.5 to about 20 weight percent, or in the range of from 3 to 10 weight percent, based on the total weight of the resulting randomization medium in randomization zone 151. The randomization medium can have any residence time in randomization zone 151 suitable to achieve the desired level of randomization. In one embodiment, the randomization medium can have a residence time in randomization zone 151 in the range of from about 1 min. to about 48 hours, in the range of from about 30 min. to about 24 hours, or in the range of from 2 to 12 hours. Additionally, the temperature in randomization zone 151 during randomization can be any temperature suitable to achieve the desired level of randomization. In one embodiment, the temperature in randomization zone 151 during randomization can be in the range of from about 20 to about 120° C., in the range of from about 30 to about 100° C., or in the range of from 50 to 80° C.

Those skilled in the art will understand that the DS and DP of the cellulose ester random copolymer might be less than that of the cellulose ester non-random copolymer. Accordingly, in this embodiment the non-random cellulose ester entering randomization zone 151 may optionally have a greater DS and/or DP than the target DS and/or DP of the randomized cellulose ester.

In one embodiment of the present invention, it may be desirable to produce cellulose esters that are at least partially soluble in acetone. Accordingly, the initial cellulose ester produced in esterification zone 140 can bypass optional randomization zone 151, thereby producing a final non-random cellulose ester. Non-random cellulose esters prepared by the methods of the present invention can be at least partially soluble in acetone when they have a DS in the range of from about 2.1 to about 2.4, in the range of from about 2.28 to about 2.39 or in the range of from 2.32 to 2.37. In one embodiment, cellulose esters produced in accordance with the present invention can have an acetone solubility rating (as defined in Example 15, below) of 3 or less, 2 or less, or 1.

After optional randomization, an optionally randomized medium can be withdrawn from randomization zone 151 via line 182. The optionally randomized medium can comprise randomized cellulose ester and residual randomizing agent. In one embodiment, the optionally randomized medium in line 182 can comprise randomized cellulose ester in an amount in the range of from about 2 to about 80 weight percent, in the range of from about 10 to about 60 weight percent, or in the range of from 20 to 40 weight percent based on the weight of the ionic liquid. Additionally, the optionally randomized medium can comprise residual randomizing agent in the range of from about 0.5 to about 20 weight percent, or in the range of from 3 to 10 weight percent, based on the total weight of the resulting randomized medium.

Additionally, the optionally randomized medium in line 182 can comprise other components, such as those described above with reference to the esterified medium in line 180 and with reference to the esterified medium in line 80 of FIG. 1. Such components include, but are not limited to, altered ionic liquid, residual acylating reagent, one or more carboxylic acids, and/or one or more catalysts.

Following optional randomization, at least a portion of the esterified and optionally randomized medium in line 182 can be introduced into precipitation zone 152. Precipitation zone 152 can operate to cause at least a portion of the cellulose ester from the esterified and optionally randomized medium to precipitate. Any methods known in the art suitable for precipitating a cellulose ester can be employed in precipitation zone 152. In one embodiment, a precipitating agent can be introduced into precipitation zone 152, thereby causing at least a portion of the cellulose ester to precipitate. In one embodiment, the precipitating agent can be a non-solvent for the cellulose ester. Examples of suitable non-solvents that can be employed as the precipitating agent include, but are not limited to, C₁ to C₈ alcohols, water, or a mixture thereof. In one embodiment, the precipitating agent introduced into precipitation zone 152 can comprise methanol.

The amount of precipitating agent introduced into precipitation zone 152 can be any amount sufficient to cause at least a portion of the cellulose ester to precipitate. In one embodiment, the amount of precipitating agent introduced into precipitation zone 152 can be at least about 20 volumes, at least 10 volumes, or at least 4 volumes, based on the total volume of the medium entering precipitation zone 152. The resulting precipitation medium can have any residence time in precipitation zone 152 suitable to achieve the desired level of precipitation. In one embodiment, the precipitation medium can have a residence time in precipitation zone 152 in the range of from about 1 to about 300 min., in the range of from about 10 to about 200 min., or in the range of from 20 to 100 min. Additionally, the temperature in precipitation zone 152 during precipitation can be any temperature suitable to achieve the desired level of precipitation. In one embodiment, the temperature in precipitation zone 152 during precipitation can be in the range of from about 0 to about 120° C., in the range of from about 20 to about 100° C., or in the range of from 25 to 50° C. The amount of cellulose ester precipitated in precipitation zone 152 can be at least 50 weight percent, at least 75 weight percent, or at least 95 weight percent, based on the total amount of cellulose ester in precipitation zone 152.

After precipitation in precipitation zone 152, a cellulose ester slurry can be withdrawn via line 184 comprising a final cellulose ester. The cellulose ester slurry in line 184 can have a solids content of less than about 50 weight percent, less than about 25 weight percent, or less than 1 weight percent.

At least a portion of the cellulose ester slurry in line 184 can be introduced into separation zone 153. In separation zone 153, at least a portion of the liquid content of the cellulose ester slurry can be separated from the solids portion. Any solid/liquid separation technique known in the art for separating at least a portion of a liquid from a slurry can be used in separation zone 153. Examples of suitable solid/liquid separation techniques suitable for use in the present invention include, but are not limited to, centrifugation, filtration, and the like. In one embodiment, at least 50 weight percent, at least 70 weight percent, or at least 90 weight percent of the liquid portion of the cellulose ester slurry can be removed in separation zone 153.

Furthermore, separation zone 153 can have any temperature or pressure suitable for solid liquid separation. In one embodiment, the temperature in separation zone 153 during separation can be in the range of from about 0 to about 120° C., in the range of from about 20 to about 100° C., or in the range of from 25 to 50° C.

After separation in separation zone 153, a cellulose ester wet cake can be withdrawn from separation zone 153 via line 187. The cellulose ester wet cake in line 187 can have a total solids content of at least 1 weight percent, at least 50 weight percent, or at least 75 weight percent. Additionally, the cellulose ester wet cake in line 187 can comprise cellulose ester in an amount of at least 70 weight percent, at least 80 weight percent, or at least 90 weight percent. Additionally, as will be discussed in greater detail below, at least a portion of the separated liquids from separation zone 153 can be withdrawn via line 186.

Once removed from separation zone 153, at least a portion of the cellulose ester solids from the cellulose ester wet cake can be washed in wash zone 154. Any method known in the art suitable for washing a wet cake can be employed in wash zone 154. An example of a washing technique suitable for use in the present invention includes, but is not limited to, a multi-stage counter-current wash. In one embodiment, a wash liquid that is a non-solvent for cellulose ester can be introduced into wash zone 154 via line 188 to wash at least a portion of the cellulose ester solids. Such wash liquids include, but are not limited to, a C₁ to C₈ alcohol, water, or a mixture thereof. In one embodiment, the wash liquid can comprise methanol. Additionally, as will be described in greater detail below, at least a portion of the wash liquid can be introduced into wash zone 154 via line 194.

In one embodiment, washing of the cellulose ester solids in wash zone 153 can be performed in such a manner that at least a portion of any undesired by-products and/or color bodies are removed from the cellulose ester solids and/or ionic liquid. In one embodiment, the non-solvent wash liquid can contain a bleaching agent in the range of from about 0.001 to about 50 weight percent, or in the range of from 0.01 to 5 weight percent based on the total weight of the wash fluid. Examples of bleaching agents suitable for use in the present invention include, but are not limited to, chlorites, such as sodium chlorite (NaClO₂); hypohalites, such as NaOCl, NaOBr and the like; peroxides, such as hydrogen peroxide and the like; peracids, such as peracetic acid and the like; metals, such as Fe, Mn, Cu, Cr and the like; sodium sulfites, such as sodium sulfite (Na₂SO₃), sodium metabisulfite (Na₂S₂O₅), sodium bisulfite (NaHSO₃) and the like; perborates, such as sodium perborate (NaBO₃.nH₂O where n=1 or 4); chlorine dioxide (ClO₂); oxygen; and ozone. In one embodiment, the bleaching agent employed in the present invention can include hydrogen peroxide, NaOCl, sodium chlorite and/or sodium sulfite. Washing in wash zone 153 can be sufficient to remove at least 50, at least 70, or at least 90 percent of the total amount of byproducts and/or color bodies.

After washing in wash zone 154, a washed cellulose ester product can be withdrawn via line 189. The washed cellulose ester product in line 189 can be in the form of a wet cake, and can comprise solids in an amount of at least 1, at least 50, or at least 75 weight percent. Additionally, the washed cellulose ester product in line 189 can comprise cellulose ester in an amount of at least 1, at least 50, or at least 75 weight percent.

The washed cellulose ester product can optionally be dried in drying zone 155. Drying zone 155 can employ any drying methods known in the art to remove at least a portion of the liquid content of the washed cellulose ester product. Examples of drying equipment suitable for use in drying zone 155 include, but are not limited to, rotary dryers, screw-type dryers, paddle dryers, and/or jacketed dryers. In one embodiment, drying in drying zone 155 can be sufficient to produce a dried cellulose ester product comprising less than 5, less than 3, or less than 1 weight percent liquids.

After drying in drying zone 155, a final cellulose ester product can be withdrawn via line 190. The final cellulose ester product in line 190 can be substantially the same as the final cellulose ester product in line 90, as described above with reference to FIG. 1.

Referring still to FIG. 2, as mentioned above at least a portion of the separated liquids generated in separation zone 153 can be withdrawn via line 186 as a recycle stream. The recycle stream in line 186 can comprise altered ionic liquid, one or more carboxylic acids, residual modifying agent, residual catalyst, residual acylating reagent, residual randomizing agent, and/or residual precipitation agent. As used herein, the term “altered ionic liquid” refers to an ionic liquid that has previously passed through a cellulose esterification step wherein at least a portion of the ionic liquid acted as acyl group donor and/or recipient. As used herein, the term “modified ionic liquid” refers to an ionic liquid that has previously been contacted with another compound in an upstream process step. Therefore, altered ionic liquids are a subset of modified ionic liquids, where the upstream process step is cellulose esterification.

In one embodiment, the recycle stream in line 186 can comprise altered ionic liquid, one or more carboxylic acids, one or more alcohols, and/or water. In one embodiment, the recycle stream in line 186 can comprise altered ionic liquid in an amount in the range of from about 10 to about 99.99 weight percent, in the range of from about 50 to about 99 weight percent, or in the range of from 90 to 98 weight percent, based on the total weight of the recycle stream in line 186. In one embodiment, the altered ionic liquid can comprise an ionic liquid having at least two different anions: primary anions and secondary anions. At least a portion of the primary anions in the altered ionic liquid originate from the initial ionic liquid introduced into dissolution zone 120 via line 164, as described above. Additionally, at least a portion of the secondary anions in the altered ionic liquid originate from the acylating reagent introduced into esterification zone 140, as described above. In one embodiment, the altered ionic liquid can comprise primary anions and secondary anions in a ratio in the range of from about 100:1 to about 1:100, in the range of from about 1:10 to about 10:1, or in the range of from 1:2 to about 2:1. Additionally, the altered ionic liquid can comprise a plurality of cations, such as those described above with reference to the initial ionic liquid in line 68 of FIG. 1.

The recycle stream in line 186 can comprise a total amount of carboxylic acids in an amount in the range of from about 5 to about 60 weight percent, in the range of from about 10 to about 40 weight percent, or in the range of from 15 to 30 weight percent based on the total weight of ionic liquid in the recycle stream in line 186. Examples of suitable carboxylic acids the recycle stream in line 186 can comprise include, but are not limited to, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid, substituted benzoic acids, phthalic acid, and isophthalic acid. In one embodiment, at least 50 weight percent, at least 70 weight percent, or at least 90 weight percent of the carboxylic acids in the recycle stream in line 186 are acetic, propionic, and/or butyric acids.

Furthermore, the recycle stream in line 186 can comprise a total concentration of alcohols in an amount of at least 20 volumes, at least 10 volumes, or at least 4 volumes, based on the total volume of the recycle stream. Examples of suitable alcohols the recycle stream in line 186 can comprise include, but are not limited to, C₁ to C₈ straight- or branched-chain alcohols. In one embodiment, at least 50 weight percent, at least 70 weight percent, or at least 90 weight percent of the alcohol in the separated ionic liquids in line 186 comprises methanol. Moreover, the recycle stream in line 186 can comprise water in an amount of at least 20 volumes, at least 10 volumes, or at least 4 volumes, based on the total volume of the recycle stream.

As depicted in FIG. 2, at least a portion of the recycle stream in line 186 can be introduced into ionic liquid recovery/treatment zone 160. Ionic liquid recovery/treatment zone 160 can operate to segregate and/or reform at least a portion of the recycle stream from line 186. In one embodiment, at least a portion of the recycle stream can undergo at least one flash vaporization and/or distillation process to remove at least a portion of the volatile components in the recycle stream. At least 40 weight percent, at least 75 weight percent, or at least 95 weight percent of the volatile components in the recycle stream can be removed via flash vaporization. The volatile components removed from the recycle stream can comprise one or more alcohols. In one embodiment, the volatile components can comprise methanol. After vaporization, the resulting volatiles-depleted recycle stream can comprise a total amount of alcohols in the range of from about 0.1 to about 60 weight percent, in the range of from about 5 to about 55 weight percent, or in the range of from 15 to 50 weight percent.

In one embodiment, at least a portion of the carboxylic acids can be removed from the recycle stream. This can be accomplished by first converting at least a portion of the carboxylic acids to carboxylate esters. In this embodiment, at least a portion of the recycle stream can be placed into a pressurized reactor where the recycle stream can be treated at a temperature, pressure, and time sufficient to convert the at least a portion of the carboxylic acid to methyl esters, by reacting the carboxylic acids with the alcohol present in the recycle stream. During the esterification, the pressurized reactor can have a temperature in the range of from 100 to 180° C., or in the range of from 130 to 160° C. Additionally, the pressure in the pressurized reactor during esterification can be in the range of from about 10 to about 1,000 pounds per square inch gauge (“psig”), or in the range of from 100 to 300 psig. The recycle stream can have a residence time in the pressurized reactor in the range of from about 10 to about 1,000 minutes, or in the range of from 120 to 600 minutes. Prior to the above-described esterification, the alcohol and carboxylic acid can be present in the recycle stream in a molar ratio in the range of from about 1:1 to about 30:1, in the range of from about 3:1 to about 20:1, or in the range of from 5:1 to 10:1 alcohol-to-carboxylic acid. In one embodiment, at least 5, at least 20, or at least 50 mole percent of the carboxylic acids can be esterified during the above-described esterification.

As mentioned above, at least a portion of the carboxylic acids can be acetic, propionic, and/or butyric acids. Additionally, as mentioned above, the alcohol present in the recycle stream can be methanol. Accordingly, the above-described esterification process can operate to produce methyl acetate, methyl propionate, and/or methyl butyrate. Subsequent to esterification, at least 10, at least 50, or at least 95 weight percent of the resulting carboxylate esters can be removed from the recycle stream by any methods known in the art. As depicted in FIG. 2, at least a portion of the carboxylate esters produced by the above described esterification can be routed to esterification zone 140 via line 196. Carboxylate esters introduced into esterification zone 140 can be employed as immiscible cosolvents, as described above. In another embodiment, at least a portion of the carboxylate esters can be converted to anhydrides by CO insertion.

In another embodiment of the present invention, at least a portion of the altered ionic liquid present in the recycle stream can undergo reformation. Reformation of the altered ionic liquid can optionally be performed simultaneously with the esterification of the carboxylic acids in the recycle stream. Alternatively, reformation of the altered ionic liquid can be performed subsequently to the esterification of the carboxylic acids in the recycle stream. Reformation of the altered ionic liquid can comprise at least one anion exchange process.

In one embodiment, reformation of the altered ionic liquid can comprise anion homogenization via anion exchange, such that substantially all of the anions of the altered ionic liquid are converted to the same type of anion. In this embodiment, at least a portion of the altered ionic liquid can be contacted with at least one alkyl formate. Alkyl formates suitable for use in the present invention include, but are not limited to, methyl formate, ethyl formate, propyl formate, isopropyl formate, butyl formate, isobutyl formate, tert-butyl formate, hexyl formate, octyl formate, and the like. In one embodiment, the alkyl formate can comprise methyl formate. Additionally, reformation of the altered ionic liquid can be performed in the presence of one or more alcohols. Alcohols suitable for use in this embodiment of the invention include, but are not limited to, alkyl or aryl alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenol and the like. In one embodiment, the alcohol present during reformation can comprise methanol.

The temperature during reformation of the altered ionic liquid can be in the range of from about 100 to about 200° C., or in the range of from 130 to about 170° C. Additionally, the pressure during reformation of the altered ionic liquid can be at least 700 kPa, or at least 1,025 kPa. Furthermore, the reaction time of the reformation of the altered ionic liquid can be in the range of from about 10 min. to about 24 hours, or in the range of from 3 to 18 hours.

As mentioned above, reformation of the altered ionic liquid can comprise anion homogenization. In one embodiment, the resulting reformed ionic liquid can have an at least 90, at least 95, or at least 99 percent uniform anion content. Additionally, the reformed ionic liquid can comprise an alkyl amine formate. In one embodiment, the amine of the alkyl amine formate can be an imidazolium. Examples of alkyl amine formates suitable for use as the reformed ionic liquid include, but are not limited to, 1-methyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium formate, 1-propyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium formate, 1-hexyl-3-methylimidazolium formate, and/or 1-octyl-3-methylimidazolium formate.

Following reformation, at least a portion of the volatile components of the reformed ionic liquid can optionally be removed via any methods known in the art for removing volatile components. Volatile components removed from the reformed ionic liquid can include, for example, carboxylate esters, such as those formed via the above described carboxylic acid esterification process. Thereafter, at least a portion of the reformed ionic liquid can undergo at least one anion exchange process to replace at least a portion of the anions of the reformed ionic liquid thereby forming a carboxylated ionic liquid. In one embodiment, the reformed ionic liquid can be contacted with at least one carboxylate anion donor to at least partially effect the anion exchange. Carboxylate anion donors suitable for use in this embodiment include, but are not limited to, one or more carboxylic acids, anhydrides, or alkyl carboxylates. Additionally, the carboxylate anion donors can comprise one or more C₂ to C₂₀ straight- or branched-chain alkyl or aryl carboxylic acids, anhydrides, or methyl esters. Furthermore, the carboxylate anion donor can be one or more C₂ to C₁₂ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters. Moreover, the carboxylate anion donor can be one or more C₂ to C₄ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters. The resulting carboxylated ionic liquid can be substantially the same as the carboxylated ionic liquid described above with reference to the carboxylated ionic liquid in line 64 of FIG. 1.

When contacting the reformed ionic liquid with one or more carboxylate anion donors, the contacting can be carried out in a contact mixture further comprising alcohol or water. In one embodiment, the alcohol or water can be present in the contact mixture in the range of from 0.01 to 20 molar equivalents per alkyl amine formate, or in the range of from 1 to 10 molar equivalents per alkyl amine formate. In one embodiment, methanol can be present in the contact mixture in the range of from 1 to 10 molar equivalents per alkyl amine formate.

Referring still to FIG. 2, in one embodiment at least a portion of the carboxylated ionic liquid produced in ionic liquid recovery/treatment zone 160 can be in a treated ionic liquid mixture further comprising at least one alcohol, at least one residual carboxylic acid, and/or water. The one or more alcohols and/or residual carboxylic acids can be substantially the same as described above with reference to the recycle stream in line 186. The treated ionic liquid mixture can be subjected to at least one liquid/liquid separation process to remove at least a portion of the one or more alcohols. Such separation process can comprise any liquid/liquid separation process known in the art, such as, for example, flash vaporization and/or distillation. Additionally, the treated ionic liquid mixture can be subjected to at least one liquid/liquid separation process to remove at least a portion of the water. Such separation process can comprise any liquid/liquid separation process known in the art, such as, for example, flash vaporization and/or distillation.

In one embodiment, at least 50, at least 70, or at least 85 weight percent of the alcohols and/or water can be removed from the treated ionic liquid mixture thereby producing a recycled carboxylated ionic liquid. At least a portion of the alcohol separated from the treated ionic liquid mixture can optionally be removed from ionic liquid recovery/treatment zone 160 via line 194. The one or more alcohols in line 194 can thereafter optionally be routed to various other points depicted in FIG. 2. In one embodiment, at least 50, at least 70, or at least 90 weight percent of the alcohols removed from the treated ionic liquid mixture can be routed to various other points in the process depicted in FIG. 2. In one optional embodiment, at least a portion of the alcohols in line 194 can be routed to randomization zone 151 to be employed as a randomizing agent. In another optional embodiment, at least a portion of the alcohols in line 194 can be routed to precipitation zone 152 to be employed as a precipitating agent. In yet another optional embodiment, at least a portion of the alcohols in line 194 can be routed to wash zone 154 to be employed as a wash liquid.

In one embodiment, at least a portion of the water separated from the treated ionic liquid mixture can optionally be removed from ionic liquid recovery/treatment zone 160 via line 192. Optionally, at least a portion of the water removed from ionic liquid recovery/treatment zone 160 can be routed to modification zone 110 to be employed as a modifying agent. At least about 5, at least about 20, or at least 50 weight percent of the water separated from the treated ionic liquid mixture can optionally be routed to modification zone 110. Additionally, at least a portion of the water in line 192 can optionally be routed to a waste water treatment process.

After alcohol and/or water removal, the above-mentioned recycled carboxylated ionic liquid can comprise residual carboxylic acid in an amount in the range of from about 0.01 to about 25 weight percent, in the range of from about 0.05 to about 15 weight percent, or in the range of from 0.1 to 5 weight percent based on the entire weight of the recycled carboxylated ionic liquid. Additionally, the recycled carboxylated ionic liquid can comprise sulfur in an amount of less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw. Furthermore, the recycled carboxylated ionic liquid can comprise halides in an amount less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw. Moreover, the carboxylated ionic liquid can comprise transition metals in an amount less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw.

In one embodiment, at least a portion of the recycled carboxylated ionic liquid produced in ionic liquid recovery/treatment zone 160 can optionally be routed to dissolution zone 120. At least 50 weight percent, at least 70 weight percent, or at least 90 weight percent of the recycled carboxylated ionic liquid produced in ionic liquid recovery/treatment zone 160 can be routed to dissolution zone 120.

In dissolution zone 120, the recycled carboxylated ionic liquid can be employed either individually or combined with the carboxylated ionic liquid entering dissolution zone 120 via line 164 to thereby form the above-described cellulose dissolving ionic liquid. In one embodiment, the recycled carboxylated ionic liquid can make up in the range of from about 10 to about 99.99 weight percent, in the range of from about 50 to about 99 weight percent, or in the range of from about 90 to about 98 weight percent of the cellulose dissolving ionic liquid in dissolution zone 120.

This invention can be further illustrated by the following examples of embodiments thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

EXAMPLES Materials Used in Examples

Commercial grades of ionic liquids employed in the following examples were manufactured by BASF and were obtained through Fluka. These ionic liquids were used both as received and after purification as described in the examples. Experimental alkyl imidazolium carboxylates were also prepared as described in the examples. Cellulose was obtained from Aldrich. The degree of polymerization of the Aldrich cellulose (DP ca. 335) was determined capillary viscometry using copper ethylenediamine (Cuen) as the solvent. Prior to dissolution in ionic liquids, the cellulose was typically dried for 14-18 h at 50° C. and 5 mm Hg, except in cases where the cellulose was modified with water prior to dissolution.

Example 1 Preparation of Cellulose Ester (Comparative)

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters giving five ports, was equipped for mechanical stirring, with an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA), and with an N₂/vacuum inlet. To the flask was added 61 g of 1 -butyl -3-methylimidazolium chloride. Prior to adding the [BMIm]Cl, the ionic liquid was melted at 90° C. then stored in a desiccator; during storage, the [BMIm]Cl remained a liquid. While stirring rapidly, began adding 3.21 g of previously dried microcrystalline cellulose (DP ca. 335) in small portions (3 min addition). The slurry was stirred for 5 min before applying vacuum. After ca. 3 h 25 min, most of the cellulose had dissolved except for a few small pieces and 1 large piece stuck to the probe. After 5.5 h, the oil bath temperature was increased to 105° C. to speed up dissolution of the remaining cellulose. The solution was maintained at 105° C. for 1.5 h (47 min heat up) before allowing the solution to cool to room temperature (6 h 25 min from the start of the cellulose addition) and stand overnight at ambient temperature.

After standing overnight, the cellulose/[BMIm]Cl solution was clear and the IR spectra indicated that all of the cellulose was dissolved. The solution was heated to 80° C. before adding 10.11 g (5 eq) Ac₂O drop wise (26 min addition). The reaction was sampled throughout the reaction period by removing 6-10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed 2× with 100 mL portions of MeOH then 2× with 100 mL of MeOH containing 8% of 35 wt % H₂O₂ before drying at 60° C., 5 mm Hg. The 1^(st) sample was white, the 2^(nd) sample was tan, and the 3^(rd) sample was brown. During the course of the reaction, the solution became progressively darker. Approximately 2 h 45 min after the start of the Ac₂O addition, the viscosity of the reaction mixture abruptly increased then the reaction mixture completely gelled. The oil bath was lowered and the contact solution was allowed to cool to room temperature.

FIG. 3 is a plot of absorbance versus time for Example 1 and it shows the dissolution of cellulose (1046 cm⁻¹) and the removal of residual water (1635 cm⁻¹) from the mixture during the course of the dissolution. The spikes in the cellulose trend line are due to large cellulose gel particles sticking to the probe which, are removed by the stirring action. Clumping occurs because the surfaces of the cellulose particles become partially dissolve before dispersion is obtained leading to clumping and large gel particles. The dip in the trend lines near 6 h result from the temperature increase from 80 to 105° C. This figure illustrates that ca. 6 h is required to fully dissolve the cellulose when the cellulose is added to the ionic liquid that is preheated to 80° C.

FIG. 4 is a plot of absorbance versus time for Example 1 and it illustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), the consumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid (1706 cm⁻¹) during the experiment. The DS values shown in FIG. 4 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. As illustrated, ca. 75% of the acetylation occurred during the first hour after which the reaction rates slowed. Approximately 2 h 45 from beginning the Ac₂O addition (DS=2.45), the solution viscosity suddenly increased followed by gellation of the contact mixture. At this point, no further reaction occurred and the remaining contact solution was processed as described above. It should be noted that there was still a large excess of Ac₂O at the point of gellation. Furthermore, during the course of the contact period, the solution became progressively darker and the final product color was dark brown. In addition to determining the DS of each sample, the molecular weight of each sample was determined by GPC (Table 1, below). In general, Mw was approximately 55,000 and the polydispersity ranged from 3-4. Based on the DP of the starting cellulose, this analysis indicates that the molecular weight of the cellulose polymer remained essentially intact during the contact period.

Example 2 Modification of Cellulose with Water

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters giving five ports, was equipped for mechanical stirring, with an iC10 diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask was added 64.3 g of 1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator; the [BMIm]Cl remained a liquid during storage. To the ionic liquid was added 3.4 g (5 wt %) of microcrystalline cellulose (DP ca. 335) at ambient temperature while stirring rapidly to disperse the cellulose. Approximately 12 min after adding the cellulose, a preheated 80° C. oil bath was raised to the flask. After ca. 17 min in the 80° C. oil bath, visually, all of the cellulose appeared to be dissolved. After ca. 22 min in the 80° C. oil bath, began applying vacuum. To insure complete removal of water, 50 min after applying vacuum, the oil bath setting was increased to 105° C. and the solution was stirred for 2 h 25 min before the oil bath was allowed to cool to room temperature.

The temperature of the clear, amber cellulose solution was adjusted to 80° C. before adding 6.42 g of Ac₂O (3 eq) drop wise (5 min addition). The contact mixture was sampled throughout the reaction period by removing 6-10 g aliquots of the contact mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed 1× with 100 mL of MeOH then 2× with MeOH containing 8 wt % 35% H₂O₂. The samples were then dried at 60° C., 5 mm Hg overnight. During the course of the contact period, the color of the solution became darker ultimately becoming dark brown. Approximately 2 h 10 min from the start of Ac₂O addition, the solution viscosity began to increase significantly; 10 min later the solution completely gelled out and started climbing the stir shaft. The experiment was aborted and MeOH was added to the flask to precipitate the remaining product.

The precipitation and the wash liquids from each aliquot were combined and concentrated invacuo at 68° C. until the vacuum dropped to 24 mm Hg which provided 54.2 g of recovered [BMIm]Cl. Analysis by ¹H NMR revealed that the ionic liquid contained 4.8 wt % acetic acid when measured by this technique.

FIG. 5 is a plot of absorbance versus time for Example 2 and it shows the dissolution of cellulose (1046 cm⁻¹) and the removal of residual water (1635 cm⁻¹) from the mixture during the course of the dissolution. As can be seen, the dissolution of the cellulose was very rapid (17 min versus 360 min in Example 1). This was due to adding the cellulose to the ionic liquid at room temperature, stirring to get a good dispersion (higher surface area), then heating to effect dissolution. Normally, [BMIm]Cl is a solid that melts at ca. 70° C. However, if water or a carboxylic acid is allowed to mix with [BMIm]Cl, the [BMIm]Cl will remain a liquid at room temperature thus allowing introduction of the cellulose at ambient temperature. As can be seen from the water loss in FIG. 5, the [BMIm]Cl contained significant water. This example illustrates that the addition of water to an ionic liquid followed by cellulose addition and good mixing to get a good dispersion provides rapid dissolution of cellulose.

FIG. 6 is a plot of absorbance versus time for Example 2 and it illustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), the consumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid (1706 cm⁻¹) during the experiment. The DS values shown in FIG. 6 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. Relative to Example 1, the reaction rate was slower (Example 1, DS=2.44@165 min; Example 2, DS=2.01@166 min, cf. Table 1, below). As was observed in Example 1, the solution viscosity suddenly increased followed by gellation of the contact mixture, but in Example 2, gellation occurred at a lower DS. Both the slower reaction rate and gellation at a lower temperature can be attributed to the use of less Ac₂O. However, it should be noted that there was still a large excess of Ac₂O at the point of gellation. As with Example 1, during the course of the contact period, the solution became progressively darker and the final product color was dark brown. In addition to determining the DS of each sample, the molecular weight of each sample was determined by GPC (Table 1, below). In general, Mw was approximately 55,000 and the polydispersity ranged from 3-6. Based on the DP of the starting cellulose, this analysis indicates that the molecular weight of the cellulose polymer remained essentially intact during the contact period.

Example 3 MSA Secondary Component, No Modification with Water

Cellulose (3.58 g, 5 wt %) was dissolved in 68 g of [BMIm]Cl in a manner similar to Example 2. To the cellulose solution (contact temperature=80° C.) was added a mixture of 433 mg MSA and 6.76 g of Ac₂O (3 eq) drop wise (8 min). The reaction was sampled throughout the reaction period by removing 6-10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed 2× with 100 mL portions of MeOH then dried at 60° C., 5 mm Hg. The solid samples were snow white. After ca. 2 h, all of the Ac₂O appeared to be consumed by IR. The experiment was aborted and the remaining sample was processed as above.

The precipitation and the wash liquids from each aliquot were combined and concentrated invacuo at 68° C. until the vacuum dropped to 24 mm Hg which provided 64 g of recovered [BMIm]Cl. Unlike Example 2, analysis by ¹H NMR revealed that the ionic liquid did not contain any acetic acid when measured by this technique. This result indicates that MSA aids in the removal of residual acetic acid from the ionic liquid, probably by conversion of the residual acetic acid to methyl acetate.

FIG. 7 is a plot of absorbance versus time for Example 3 and it illustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), the consumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid (1706 cm⁻¹) during the experiment. The DS values shown in FIG. 7 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. What is apparent from FIG. 7 is that the rates of reaction are much faster compared to Examples 2 and 3. For example, 55 min was required to reach a DS of 1.82 in Example 1-1 (Table 1, below) while only 10 min was required to reach a DS of 1.81 in Example 3-1. Similarly, 166 min was required to reach a DS of 2.01 in Example 2-4 (Table 1, below) while only 20 min was required to reach a DS of 2.18 in Example 3-2. Additionally, FIG. 7 shows that no gellation occurred during the course of the experiment. In fact, through out the experiment, there was not any increase in solution viscosity, the solution color was essentially unchanged from the initial solution color, and the products isolated from the contact mixture were all snow white. Finally, it should be noted in Table 1, below, that the Mw (ca. 40,000) for the samples of Example 3 are less than those for Examples 1 and 2 and that the polydispersity (Mw/Mn) is lower and more narrow (2-3) than those for Examples 1 and 2 (3-6). When compared to Examples 1 and 2, Example 3 shows that inclusion of a secondary component such as MSA in the contact mixture accelerates the rates of reaction, significantly improves solution and product color, prevents gellation of the contact mixture, allows the achievement of high DS values while using less acylating reagent, and helps to promote lowering of the cellulose ester molecular weight.

TABLE 1 Properties of Cellulose Acetates Prepared Without Water Modification Example Time (min) DS Mw Mw/Mn 1-1 55 1.82 59243 3.29 1-2 122 2.25 61948 4.34 1-3 165 2.44 51623 3.73 2-1 6 0.64 50225 2.93 2-2 34 1.49 56719 3.48 2-3 56 1.73 64553 5.4 2-4 166 2.01 66985 5.7 2-5 176 2.05 63783 5.83 3-1 10 1.81 41778 1.92 3-2 20 2.18 43372 2.01 3-3 27 2.39 41039 2.22 3-4 43 2.52 41483 2.4 3-5 66 2.62 40412 2.54 3-6 124 2.72 39521 2.55

Example 4 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters giving five ports, was equipped for mechanical stirring, with an iC10 diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added 58.07 g of 1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator. The flask was placed in an oil bath and heated to 80° C.

To 3.06 g (5 wt %) of microcrystalline cellulose (DP ca. 335), was added 3.06 g of water. The slurry was hand mixed and allowed to stand for ca. 30 min before adding the slurry in small portions to the [BMIm]Cl (5 min addition). This gave a hazy solution in which the cellulose was surprisingly well dispersed. The slurry was stirred for 27 min, before applying vacuum. Visually, after 28 min under vacuum all of the cellulose had dissolved which was confirmed by IR. By IR, there was still ca. 3 wt % water in the [BMIm]Cl when all of the cellulose was dissolved. The system was maintained under vacuum at 80° C. to remove the remaining water. The sample was allowed to cool to room temperature and left standing until the next step.

The cellulose solution was heated to 80° C. before adding a mixture of 5.78 g Ac₂O (3 eq) and 368 mg MSA drop wise (8 min). The reaction was sampled throughout the reaction period by removing 6-10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed 2× with 100 mL portions of MeOH then dried at 60° C., 5 mm Hg. The isolated samples were snow white. The solution color was excellent through out the experiment and there was no indication of a viscosity increase. After ca. 2 h 25 min, infrared spectroscopy indicated that all of the Ac₂O was consumed. The experiment was aborted and the remaining sample was processed as above.

FIG. 8 is a plot of absorbance versus time for Example 4 and it shows the dissolution of cellulose (1046 cm⁻¹) and the removal of residual water (1635 cm⁻¹) from the mixture during the course of the dissolution. As can be seen, the dissolution of the water wet (activated) cellulose was very rapid (28 min) despite the presence of a significant amount of water. This is surprising in view of the conventional teachings. The addition of water wet cellulose to the ionic liquid enables one to obtain a good dispersion of cellulose with little clumping. Upon application of a vacuum to remove the water, the cellulose rapidly dissolves without clumping to form large particles.

FIG. 9 is a plot of absorbance versus time for Example 4 and it illustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), the consumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid (1706 cm⁻¹) during the experiment. The DS values shown in FIG. 9 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. Relative to Example 3, the reaction rate to produce cellulose acetate was similar. However, the molecular weights (ca. 33,000) of the cellulose acetate samples (Table 2, below) were notably lower that that observed in Example 3 and much lower than that observed in Examples 1 and 2 (Table 1, above). Additionally, the polydispersities for the samples of Example 4 are all less than 2, less than that observed for the samples of Examples 1, 2, and 3.

This example illustrates that water wet cellulose leads to good cellulose dispersion in the ionic liquid and rapid cellulose dissolution. The reaction rate for formation of cellulose acetate is rapid. Surprisingly, water wet cellulose leads to lower molecular weight cellulose acetate with low polydispersities relative to dry cellulose. The cellulose acetate made from water wet cellulose has better acetone solubility relative to when dry cellulose is utilized.

Example 5 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters giving five ports, was equipped for mechanical stirring, with a iC10 diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added 67.33 g of 1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator. The flask was placed in an oil bath and heated to 80° C. To 7.48 g (10 wt %) of microcrystalline cellulose (DP ca. 335), was added 7.08 g of water. The cellulose slurry was hand mixed and allowed to stand for ca. 60 min before adding the slurry in small portions to the [BMIm]Cl (8 min addition). This gave a hazy solution in which the cellulose was surprisingly well dispersed. The slurry was stirred for 10 min, before applying vacuum. The cellulose dissolution was left stirring overnight.

Infrared spectroscopy indicated that essentially all of the cellulose was dissolved within 50 min after applying vacuum; ca. 3.5 h was required to remove the water. To the cellulose solution was added a mixture of 14.13 g of Ac₂O (3 eq) and 884 mg (0.2 eq) of MSA drop wise (11 min). The reaction was sampled throughout the reaction period by removing 6-10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed 2× with 100 mL portions of MeOH then dried at 60° C., 5 mm Hg. The isolated samples were snow white. The solution color was excellent through out the experiment and there was no indication of a viscosity increase. After ca. 2 h 10 min, all of the Ac₂O appeared to be consumed by IR. The experiment was aborted and the remaining sample was processed as above.

FIG. 10 is a plot of absorbance versus time for Example 5 and it shows the dissolution of cellulose (1046 cm⁻¹) and the removal of residual water (1635 cm⁻¹) from the mixture during the course of the dissolution. As can be seen, the dissolution of the water wet (activated) cellulose was very rapid (50 min) despite the presence of a significant amount of water and the increase in cellulose concentration relative to Example 4.

FIG. 11 is a plot of absorbance versus time for Example 5 and it illustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), the consumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid (1706 cm⁻¹) during the experiment. The DS values shown in FIG. 11 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. Despite the increase in cellulose concentration, relative to Examples 3 and 4, the reaction rate to produce cellulose acetate was similar. The molecular weights (ca. 22,000) of the cellulose acetate samples (Table 2, below) were notably lower that that observed in Example 4 and much lower than that observed in Examples 1, 2, and 3 (Table 1, above). As was observed for Example 4, the polydispersities for the samples of Example 5 are all less than 2, less than that observed for the samples of Examples 1, 2, and 3.

This example illustrates that water wet cellulose leads to good cellulose dispersion in the ionic liquid and rapid cellulose dissolution even when the cellulose concentration is increased to 10 wt %. The reaction rate for formation of cellulose acetate is rapid. Surprisingly, water wet cellulose at this concentrations leads to even lower molecular weight cellulose acetates with low polydispersities relative to dry cellulose. The cellulose acetate made from water wet cellulose has better acetone solubility relative to when dry cellulose is utilized.

Example 6 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters giving five ports, was equipped for mechanical stirring, with an iC10 diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added 51.82 g of 1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator. The flask was placed in an oil bath and heated to 80° C. To 9.15 g (15 wt %) of microcrystalline cellulose (DP ca. 335), added 53.6 g of water. After hand mixing, the cellulose was allowed to stand in the water for 50 min before filtering which gave 18.9 g of a wet cellulose cake. The water wet cellulose was then added in small portions to the [BMIm]Cl (5 min addition). Within 2 min, the cellulose was finely dispersed in the ionic liquid. Ten minutes after adding the cellulose to the [BMIm]Cl, the flask was placed under vacuum. After ca. 1 h, there were no visible cellulose particles; the solution viscosity was very high and the solution started climbing the stir rod. The solution was left stirring overnight at 80° C. under vacuum.

Infrared spectroscopy indicated that ca. 1 h was required for cellulose dissolution and 2 h was required to strip the water to the initial value. The cellulose solution was heated to 100° C. prior to adding a mixture of 17.28 g Ac₂O (3 eq) and 1.087 g (0.2 eq) of MSA drop wise (8 min). The reaction was sampled throughout the reaction period by removing 6-10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed 1× with 100 mL of MeOH then 2× with MeOH containing 8 wt % 35% H₂O₂. The solid samples were then dried at 60° C., 5 mm Hg. After ca. 65 min, all of the Ac₂O appeared to be consumed by IR. The experiment was aborted and the remaining sample was processed as above.

FIG. 12 is a plot of absorbance versus time for Example 6 and it shows the dissolution of presoaked water wet cellulose (1046 cm⁻¹) and the removal of residual water (1635 cm⁻¹) from the mixture during the course of the dissolution. As can be seen, the dissolution of the water wet (activated) cellulose was very rapid (60 min) despite the presence of a significant amount of water and the use of 15 wt % cellulose. Even more surprising was the rapid removal of water (ca. 2 h) at this high cellulose concentration.

FIG. 13 is a plot of absorbance versus time for Example 6 and it illustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), the consumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid (1706 cm⁻¹) during the experiment. The DS values shown in FIG. 13 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. Despite the increase in cellulose concentration (15 wt %), acetic anhydride could be easily mixed into the cellulose solution at 100° C. The higher reaction temperature led to an increase in reaction rate. Again, the molecular weights (ca. 20,000) of the cellulose acetate samples (Table 2, below) were notably lower that that observed in Examples 1, 2, and 3 (Table 1, above) were the cellulose was dried prior to use; the polydispersities for the samples of Example 6 are also less than 2.

This example illustrates that water wet cellulose leads to good cellulose dispersion in the ionic liquid and rapid cellulose dissolution even when the cellulose concentration is increased to 15 wt %. This example also shows that higher temperature (100° C.) increases reaction rates for formation of cellulose acetate. Surprisingly, water wet cellulose at this concentrations leads to even lower molecular weight cellulose acetates with low polydispersities relative to dry cellulose. The cellulose acetate made from water wet cellulose has better acetone solubility relative to when dry cellulose is utilized.

TABLE 2 Effect of Water Modification on Properties of Cellulose Acetates Example Time (min) DS Mw Mw/Mn 4-1 9 1.58 31732 1.73 4-2 13 1.94 33559 1.64 4-3 21 2.15 34933 1.63 4-4 35 2.28 31810 1.77 4-5 150 2.63 30771 1.89 5-1 11 1.95 24522 1.6 5-2 14 2.21 23250 1.67 5-3 18 2.35 22706 1.76 5-4 22 2.52 22692 1.79 5-5 31 2.59 21918 1.86 5-6 45 2.60 21628 1.89 5-7 70 2.66 19708 1.97 5-8 130 2.67 20717 1.99 6-1 10 2.63 20729 1.67 6-2 14 2.75 19456 1.78 6-3 18 2.80 19658 1.84 6-4 23 2.87 18966 1.84 6-5 32 2.89 20024 1.88 6-6 65 2.96 18962 1.85

Example 7 Miscible Cosolvent

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters giving five ports, was equipped for mechanical stirring, with an iC10 diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added 58.79 g of 1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator. The flask was placed in an oil bath and heated to 80° C. After reaching 80° C., began collecting IR spectra before adding 1.82 g (3 wt %) of glacial acetic acid. The mixture was stirred for 12 min before adding 10.38 g (15 wt %) cellulose (DP ca. 335) as a water wet cellulose cake (10.29 g water, prepared by soaking the cellulose for 50 min in excess water, 9 min addition). The mixture was stirred for ca. 9 min to allow the cellulose to disperse before applying a vacuum. After ca. 65 min, infrared spectroscopy indicated that all of the cellulose was dissolved (FIG. 14). Stirring was continued for an additional 70 min before adding 1.82 g of glacial acetic acid (6 wt % total). In order to reduce the solution viscosity, the stirring was turned off 8 min after adding the acetic acid and the oil bath temperature was increased to 100° C. After reaching 100° C. (45 min) stirring was resumed. Infrared spectroscopy indicated that upon resuming stirring, the acetic acid mixed well with the cellulose solution. The final solution was clear and no cellulose particles were observed. After standing for 10 days, the cellulose solution was still clear and could be hand stirred at room temperature which one cannot do with a 15 wt % cellulose solution in [BMIm]Cl in the absence of acetic acid.

This example shows that significant amount of a miscible cosolvent such as a carboxylic acid compatible with cellulose acylation can be mixed with a cellulose-ionic liquid sample while still maintaining cellulose solubility. A cosolvent has the added benefit of reducing solution viscosity.

Example 8 Randomization

A 3-neck 250 mL round bottom flask, fitted with two double neck adapters giving five ports, was equipped for mechanical stirring, with an iC10 diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added 149.7 g of 1-butyl-3-methylimidazolium chloride. The flask was placed in an oil bath and heated to 80° C. Microcrystalline cellulose (12.14 g, 7.5 wt %, DP ca. 335) was added to 68.9 g of water. After hand mixing, the cellulose was allowed to stand in the water for 45 min at 60° C. before filtering which gave 24.33 g of a wet cellulose cake. The water wet cellulose was then added in small portions to the [BMIm]Cl (5 min addition). Approximately 15 min after adding the cellulose to the [BMIm]Cl, the flask was placed under vacuum by gradually lowering the vacuum starting at ca. 120 mm Hg to ca. 1.4 mm Hg. After ca. 85 min, there were no visible cellulose particles; IR spectroscopy indicated that all of the cellulose was dissolved. The solution was left stirring overnight at 80° C. under vacuum.

To the cellulose solution heated to 80° C. was added a mixture of 22.93 g Ac₂O (3 eq) and 1.427 g (0.2 eq) of MSA drop wise (15 min). The reaction was sampled throughout the reaction period by removing 6-10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed 3× with 100 mL portions of MeOH then dried at 60° C., 5 mm Hg. After removing an aliquot 192 min from the start of the Ac₂O addition, 1.21 g of MeOH was added to the contact mixture. The contact mixture was stirred for an addition 120 min before adding 1.95 g of water. The contact mixture was then stirred overnight at 80° C. (14 h 40 min) at which time, the experiment was aborted and the remaining sample was processed as above.

The contact times, DS and molecular weights for isolated samples removed from the contact mixture are summarized below in Table 3.

TABLE 3 Effect of Randomization on Cellulose Acetates Example Time (min) DS Mw Mw/Mn 8-1 16 1.95 26492 1.54 8-2 18 2.15 24838 1.57 8-3 21 2.24 23973 1.63 8-4 25 2.33 23043 1.7 8-5 32 2.42 23499 1.79 8-6 57 2.56 21736 1.82 8-7 190  2.73 20452 2.08 8-8 After MeOH Addition 2.73 20478 2.00  8-10 After H₂O Addition 2.59 21005 1.89

With increasing contact time, the DS increased (until water was added) and the Mw decreased. Fifty-seven minutes after starting the contact period, the cellulose acetate sample had a DS of 2.56 and a Mw of 21,736. Prior to adding the MeOH/water, the DS was 2.73 and the Mw was 20,452. After the water contact period, the isolated cellulose acetate had a DS of 2.59 and a Mw of 21,005 indicating that the DS was reduced but the Mw was unchanged.

FIG. 15 shows the proton NMR spectra of a cellulose acetate prepared by direct acetylation (DS=2.56) and after randomization (DS=2.59). Both the ring protons attached to the anhydroglucose monomers and acetyl protons attached to the acetyl substituents are shown. FIG. 15 demonstrates that even though these two cellulose acetates have much essentially the same DS, they have a much different monomer content.

Example 9 MSA Secondary Component, Minimal Acylating Reagent

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters giving five ports, was equipped for mechanical stirring, with an iC10 diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added 60.47 g of 1-allyl-3-methylimidazolium chloride. The flask was placed in an oil bath and heated to 80° C. Microcrystalline cellulose (9.15 g, 7 wt %, DP ca. 335) was added to 27.3 g of water. After hand mixing, the cellulose was allowed to stand in the water for 50 min at 60° C. before filtering which gave 9.44 g of a wet cellulose cake. The water wet cellulose was then added in small portions to the [AMIm]Cl (5 min addition). Approximately 15 min after adding the cellulose to the [AMIm]Cl, the flask was placed under vacuum by gradually lowering the vacuum starting at ca. 120 mm Hg. After ca. 40 min, there were no visible cellulose particles; IR spectroscopy indicated that all of the cellulose was dissolved. The solution was left stirring overnight at 80° C. under vacuum.

To the cellulose solution heated to 80° C. was added a mixture of 8.58 g Ac₂O (3 eq) and 537 mg (0.2 eq) of MSA drop wise (5 min). The reaction was sampled throughout the reaction period by removing 6-10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed 3× with 100 mL portions of MeOH then dried at 60° C., 5 mm Hg. After all of the Ac₂O appeared to be consumed by IR, the experiment was aborted and the remaining sample was processed as above.

The contact times, DS and molecular weights for isolated samples removed from the contact mixture are summarized below in Table 4.

TABLE 4 Contact Times and Properties of Cellulose Acetate Prepared in [AMIm]CI. Example Time (min) DS Mw Mw/Mn 9-1 5 1.74 36192 1.69 9-2 8 2.24 35734 1.84 9-3 11 2.38 32913 1.9 9-4 15 2.48 31811 1.99 9-5 24 2.60 31970 2.14 9-6 50 2.74 31302 2.36 9-7 109 2.82 30808 2.48

Five minutes after starting the reaction, the first cellulose acetate sample had a DS of 1.74 and a Mw of 36,192. With increasing contact time, the DS increased and the Mw decreased. After 109 min, the DS was 2.82 and the Mw was 30,808. This example shows that, compared to the conventional method of Example 11 (5 eq Ac₂O, 6.5 h contact time), the method of Example 9 provides for a higher DS and a significant reduction in cellulose acetate molecular weight. For example, the conventional method of Example 11 requires 6.5 h to provide a cellulose acetate with a DS of 2.42 and a Mw of 50,839 while in Example 9, a cellulose acetate with a DS of 2.48 and a Mw of 31,811 was achieved in 15 min.

Example 10 Conventional Cellulose Ester Preparation (Comparative)

A solution of cellulose (5 wt %) dissolved in 29.17 g of [BMIm]Cl was heated to 80° C. with an oil bath. The solution was held under vacuum (ca. 7 mm Hg) while stirring for 2 h. To the cellulose solution was added 4.6 g (5 eq) of Ac₂O (5 min addition). During the course of the reaction, the solution color became gradually darker (brown). After 2.5 h, the solution had gelled so the contact solution was allowed to cool to room temperature. The product was isolated by adding the solution to water then homogenizing to give a dispersed gel/powder. The mixture was filtered and washed extensively with water. After drying the solid invacuo at 50° C., 2.04 g of a pink powder was obtained that was insoluble in acetone. Analysis by ¹H NMR indicated that the sample had a DS of 2.52 and a Mw of 73,261.

Example 11 Conventional Cellulose Ester Preparation (Comparative)

To a 3-neck 100 mL round bottom flask equipped for mechanical stirring and with an N₂/vacuum inlet added 33.8 g of 1-allyl-3-methylimidazolium chloride. While stirring rapidly, added 1.78 g of dry cellulose powder (DP ca. 335). The flask was placed under vacuum (2 mm Hg) and the mixture was stirred at room temperature to insure that the cellulose was well dispersed. After 15 min, the cellulose was well dispersed and the solution viscosity was rising. The flask was placed in an oil bath which was heated to 80° C. After 40 min, all of the cellulose was dissolved. The solution was maintained at 80° C. for 6.5 h before allowing the solution to cool to room temperature and stand overnight.

The viscous solution was heated to 80° C. before adding 5.6 g (5 eq) of Ac₂O drop wise (15 min). After 5 h, the product was isolated by pouring the mixture into 300 mL of MeOH. The MeOH/solid slurry was stirred for ca. 30 min before filtering to remove the liquids. The solid was then taken up in two 200 mL portions of MeOH and the slurry was stirred for ca. 30 min before filtering to remove the liquids. The solids were dried overnight at 55° C. (6 mm Hg) which gave 2.27 g of a powder that gave a hazy acetone solution. Analysis by ¹H NMR and by GPC indicated that the sample had a DS of 2.42 and a Mw of 50,839.

Example 12 MSA Secondary Component, Long Chain Aliphatic Cellulose Esters

A solution of cellulose (5 wt %) dissolved in [BMIm]Cl was heated to 80° C. with an oil bath. The solution was held under vacuum (ca. 2.5 mm Hg) while stirring for 4 h. To the cellulose solution was added a mixture of 10.88 g (5 eq) of nonanoic anhydride and 141 mg of MSA (25 min addition). After 18.5 h, the solution was allowed to cool to room temperature before it was poured into a solution of 80:20 MeOH:H₂O. After filtering the solid was washed extensively with 85:15 MeOH:H₂O then with 95:5 MeOH:H₂O. The sample was dried invacuo which gave 3.7 g of a white powder soluble in isododecane. Analysis by ¹H NMR indicated that the product was cellulose nonanoate with a DS of 2.49.

Obtainment of a cellulose nonanoate with a high degree of substitution by the method of this example is surprising in view of conventional teachings that long chain aliphatic cellulose esters with a DS greater than ca. 1.5 cannot be prepared in ionic liquids.

Example 13 MSA Secondary Component, C3 and C4 Alphatic Cellulose Esters

A solution of cellulose (5 wt %) dissolved in [BMIm]Cl was heated to 80° C. with an oil bath. The solution was held under vacuum (ca. 6 mm Hg) while stirring overnight. To the cellulose solution was added a mixture of 7.91 g (5 eq) of butyric anhydride and 190 mg of MSA (25 min addition). After 2.6 h, the solution was allowed to cool to room temperature before it was poured into water. The solid was washed extensively with water before drying invacuo which gave 2.62 g of a white powder soluble in acetone and 90:10 CHCl₃:MeOH. Analysis by ¹H NMR indicated that the product was cellulose butyrate with a DS of 2.59.

This example shows that C3 and C4 aliphatic cellulose esters with high degrees of substitution can be prepared by the methods of this example.

Example 14 Homogenization of Cellulose Solution

To a 1 L flat bottom kettle was added 193.6 g of solid [BMIm]Cl. A 3 neck top was placed on the kettle and the kettle was fitted with a N₂/vacuum inlet and for mechanical stirring. The kettle was then placed in an 80° C. oil bath and the [BMIm]Cl was melted while stirring under a 6 mm Hg vacuum. After the [BMIm]Cl was completely melted, 10.2 g of previously dried cellulose (DP ca. 335) was added and the mixture was homogenized with a Heidolph Silent Crusher. After ca. 3 min of homogenization, essentially all of the cellulose was dissolved. The solution was stirred under vacuum (6 mm Hg) for an additional 1.5 h at which time, all of the cellulose was dissolved.

This example illustrates that high intensity mixing can be used to disperse the cellulose (increased surface area) which leads to rapid cellulose dissolution.

Example 15 Acetone Solubility

The solubilities of cellulose acetate in acetone were evaluated as follows: Acetone (Burdick & Jackson high purity grade) was dried prior to use using 4 A molecular sieves (purchased from Aldrich and stored in an oven at 125° C.). All of the cellulose acetates were dried prior to use in a vacuum oven (Eurotherm 91e) at 60° C., 5 mm Hg for at least 12 h. Each cellulose acetate was weighed into a 2 Dram vial (100 mg±1 mg) and 1 mL±5 μL of dry acetone was then added to the vial (vials were obtained from VWR). The vials were then placed in an ultrasonic bath (VWR, model 75HT) and ultrasonicated at room temperature for 30-120 min then removed and vortexed (VWR minivortexer) at room temperature using a speed setting of 10. If the cellulose acetate appeared to be dissolving but the rate of dissolution appeared to be slow, the vial was placed on a roller and mixed (ca. 15 revolutions per min) overnight at ambient temperature. Following the mixing period, the solubility of each cellulose acetate was rated as follows:

Rating Description 1 Soluble, transparent with no visible particles 2 Partially soluble, hazy 3 Partially soluble, very hazy, visible particles 4 Gel 5 Swollen solid 6 Insoluble Cellulose acetates with a rating of 1 are very useful in all applications in which acetone solubility or solubility in related solvents (e.g. diethyl phthalate) is a critical factor (e.g. solvent spinning of acetate fiber or melt processing of plasticized cellulose acetate). Cellulose acetates with a rating of 2 or 3 would require additional filtration to remove insoluble particles and/or the use of co-solvents before they would have utility. Cellulose acetates with a rating of 4-6 would not have utility in these applications. Hence, cellulose acetates with a rating of 1 are highly desired.

The solubility in acetone of cellulose acetates prepared in Examples 3-6, 8, 9 are compared (Table 5, below) to the solubilities of the cellulose acetates in Examples 1, 2 and to cellulose acetates (Examples 15-1 to 15-6) prepared by traditional methods. The cellulose acetates prepared by traditional methods were prepared by acetylation of cellulose to make cellulose triacetate followed by H₂SO₄ catalyzed reduction of DS, a process know to yield cellulose acetates that are random copolymers. In the absence of water (dry acetone), the acetone solubility of these cellulose acetates is known to be limited to a narrow range (from about 2.48 to about 2.52).

TABLE 5 Solubility of Cellulose Acetate in Acetone (100 mg/mL). Example DS Solubility 1-1 1.82 5 1-2 2.25 4 1-3 2.44 4 2-1 0.64 5 2-2 1.49 5 2-3 1.73 5 2-4 2.01 5 2-5 2.05 5 3-1 1.81 5 3-2 2.18 1 3-3 2.39 1 3-4 2.52 2 3-5 2.62 3 3-6 2.72 3 4-1 1.58 6 4-2 1.94 2 4-3 2.15 1 4-4 2.28 1 4-5 2.63 2 5-1 1.95 2 5-2 2.21 1 5-3 2.35 1 5-4 2.52 2 5-5 2.59 2 5-6 2.60 2 5-7 2.66 3 5-8 2.67 3 6-1 2.63 2 6-2 2.75 3 6-3 2.80 3 6-4 2.87 3 6-5 2.89 3 6-6 2.96 3 8-1 1.95 3 8-2 2.15 1 8-3 2.24 1 8-4 2.33 1 8-5 2.42 1 8-6 2.56 2 8-7 2.73 2 9-1 1.74 5 9-2 2.24 1 9-3 2.38 1 9-4 2.48 2 9-5 2.60 3 9-6 2.74 3 9-7 2.82 3 15-1  2.48 1 15-2  2.46 2 15-3  2.16 3 15-4  1.99 5 15-5  1.96 5 15-6  1.80 6

Careful examination of Table 5 reveals that the cellulose acetates having a DS from about 2.42 to about 2.15 that were produced by acetylation of cellulose dissolved in ionic liquids in the presence of a secondary component (Examples 3-6, 8, 9) all have a acetone solubility rating of 1. That is, all of these samples yield transparent acetone solutions in which there are no visible particles. In contrast, cellulose acetates produced by acetylation of cellulose dissolved in ionic liquids in the absence of a secondary component (Examples 1 and 2) have acetone solubility ratings of 4-5 regardless of DS. For example, Example 1-2 (no secondary component) has a DS of 2.25 and this cellulose acetate forms a gel in acetone while Examples 8-3 and 9-2 (includes secondary component) have a DS of 2.24 and these cellulose acetates yield transparent acetone solutions. In agreement with what is known about cellulose acetates prepared by traditional methods, only one of the cellulose acetates examined (15-1, DS=2.48) has an acetone solubility rating of 1. Example 15-3 (DS=2.16) has an acetone solubility rating of 3 as opposed to Examples 4-3 and 8-2 (DS=2.15) which have acetone solubility ratings of 1.

This example shows that cellulose acetates produced by acetylation of cellulose dissolved in ionic liquids in the presence of a secondary component having a DS of about 2.4 to about 2.1 yield transparent acetone solutions. In the absence of a secondary component, none of the cellulose acetates yield transparent acetone solutions. Furthermore, the DS range that yield transparent acetone solutions when using cellulose acetates produced by acetylation of cellulose dissolved in ionic liquids in the presence of a secondary component is broader and lower relative to cellulose acetates produced by traditional methods. Without wishing to be bound by theory, the evidence indicates that these solubility differences reflect a difference in copolymer compositions.

Example 16 Purification of [BMIm]acetate

To a 1 L 3-neck round bottom flask was added 360 mL of water, 1.30 g of acetic acid, and 5.68 g of Ba(OH)₂.H₂O. The mixture was heated to 80° C. giving a translucent solution. To this solution was added 300 g of commercial [BMIm]OAc dropwise (1 h addition) containing 0.156 wt % sulfur as determined by XRF. The solution was held at 80° C. for an addition hour before allowing the solution to cool to room temperature. The solids formed during the reaction were removed by centrifuging before concentration the solution in vacuo (60-65° C., 20-80 mm Hg) to a pale yellow liquid. The liquid was extracted with two 300 mL portions of EtOAc. The liquid was concentrated first at 60° C., 20-50 mm Hg then at 90° C., 4 mm Hg leading to 297.8 g of a pale yellow oil. Proton NMR confirmed the formation of the [BMIm]OAc which, by XRF, contained 0.026 wt % sulfur.

Example 17 Preparation of [BMIm]propionate

To a 1 L 3-neck round bottom flask was added 400 mL of water, 62.7 g of acetic acid, and 267 g of Ba(OH)₂.H₂O. The mixture was heated to 74° C. giving a translucent solution. To this solution was added 100 g of commercial [BMIm]HSO₄ dropwise (1.75 h addition). The solution was held at 74-76° C. for an addition 30 min before allowing the solution to cool to room temperature and stand overnight (ca. 14 h). The solids formed during the reaction were removed by filtration before concentration the solution in vacuo which gave an oil containing solids which formed during concentration. The solids were removed centrifuging giving an amber liquid. Additional product was obtained by slurring the solids in EtOH and centrifuging. The liquids were concentrated first at 60° C., 20-50 mmHg then at 90° C., 4 mm Hg leading to 65.8 g of an amber oil. Proton NMR confirmed the formation of the [BMIm]OPr which, by XRF, contained 0.011 wt % sulfur.

Example 18 Preparation of [BMIm]formate

To 300 mL autoclave was added 25 g of 1-butylimidazole, 45.4 g (3.75 eq) of methyl formate, and 21 mL of MeOH (2.58 eq). The autoclave was pressurized to 1035 kPa before heating the solution to 150° C. The contact solution was maintained at 150° C. for 18 h. The solution was allowed to cool to room temperature before removing the volatiles components in vacuo. Proton NMR of the crude reaction mixture revealed that 89% of the 1-butylimidazole was converted to [BMIm]formate. Purified [BMIm]formate was obtained by removal of 1-butylimidazole from the crude product by distillation.

Example 19 Conversion of [BMIm]formate to [BMIm]acetate Using Methyl Acetate

To 300 mL autoclave was added 25 g of [BMIm]formate, 50.3 g (5.0 eq) of methyl acetate, and 50 mL of MeOH (9 eq). The autoclave was pressurized to 1035 kPa before heating the solution to 170° C. The contact solution was maintained 170° C. for 15.3 h. The solution was allowed to cool to room temperature before removing the volatiles components in vacuo. Proton NMR of the reaction mixture revealed that 57% of the [BMIm]formate was converted to [BMIm]acetate.

Example 20 Conversion of [BMIm]formate to [BMIm]acetate Using Acetic Anhydride

To 25 mL single-neck round bottom flask was added 11.1 g of [BMIm]formate. Acetic anhydride (6.15 g) was added dropwise to the [BMIm]formate. Evolution of gas was noted during the addition as well as warming of the solution (47° C.). The flask was then placed in a preheated 50° C. water bath for 45 min before applying a vacuum (4 mm Hg) and heating to 80° C. to remove the volatile components. Analysis of the resulting liquid by ¹H NMR indicated 100% conversion of the starting material to [BMIm]acetate.

Example 21 Conversion of [BMIm]formate to [BMIm]acetate Using Acetic Acid

To 300 mL autoclave was added 25 g of [BMIm]formate, 87.4 g (6.3 eq) of acetic acid, and 23.1 g of MeOH (5.3 eq). The autoclave was pressurized to 1035 kPa before heating the solution to 150° C. The contact solution was maintained 150° C. for 14 h. The solution was allowed to cool to room temperature before removing the volatiles components in vacuo. Proton NMR of the reaction mixture revealed that 41% of the [BMIm]formate was converted to [BMIm]acetate.

Example 22 Conversion of [BMIm]acetate to [BMIm]formate Using Methyl Formate

To 1 L autoclave was added 100.7 g of [BMIm]acetate, 152.5 g (5 eq) of methyl formate, and 200 mL of MeOH (9.7 eq). The autoclave was pressurized to 1035 kPa before heating the solution to 140° C. The contact solution was maintained 140° C. for 18 h. The solution was allowed to cool to room temperature before removing the volatiles components in vacuo. Proton NMR of the reaction mixture revealed that 100% of the [BMIm]acetate was converted to [BMIm]formate.

Example 23 Comparison of High and Low Sulfur [BMIm]OAc

23A:

To a 100 mL 3-neck round bottom flask was added 32.75 g of commercial high sulfur [BMIm]OAc (0.156 wt % sulfur) and 1.72 g of cellulose powder. This mixture was briefly homogenized at ambient temperature before the flask was placed in a preheated 80° C. oil bath. The mixture was stirred at 80° C., 2 mm Hg for 1.75 h; ca. 15 min was required to completely dissolve the cellulose. The straw colored solution was allowed to cool to room temperature and stand under vacuum overnight (ca. 14 h).

To the mechanically stirred solution was added a solution of methane sulfonic acid (MSA, 210 mg) and acetic anhydride (5.42 g, 5 eq/AGU) dropwise (23 min). At the end of the addition, the temperature of the contact mixture was 35° C. and the solution was dark amber. After 1.5 h from the start of the addition, 5.5 g of the contact mixture was removed and the product was isolated by precipitation in MeOH. The contact mixture was then heated to 50° C. (25 min heat up time) and stirred for 1.5 h before 6.5 g of solution was removed and poured into MeOH. The remaining contact solution was heated to 80° C. (25 min heat up) and stirred for 2.5 h before pouring into MeOH. All of the solids obtained by precipitation in MeOH were isolated by filtration, washed extensively with MeOH, and dried overnight at 50° C., 5 mm Hg.

23B:

An identical reaction to 23A was conducted side-by-side using 37.02 g of low sulfur [BMIm]OAc (0.025 wt % sulfur, cf. example 1), 1.95 g of cellulose, 6.14 g of acetic anhydride, and 222 mg of MSA.

The grams of product isolated and the analysis of each product is summarized below in Table 6.

TABLE 6 Yield and Properties of CA Prepared in [BMIm]OAc Entry Yield (g) DS Mn Mw Mz 23A-RT 0.37 2.53 15123 54139 135397 23A-50° C. 0.45 2.65 12469 51688 123527 23A-80° C. 1.36 2.62 15828 85493 237785 23B-RT 0.29 0.80 14499 65744 301858 23B-50° C. 0.40 0.80 14768 57066 227833 23B-80° C. 1.26 0.76 16100 70293 325094

As can be seen from Table 6, above, the DS of the CA made using the high sulfur [BMIm]OAc as solvent was higher and the molecular weight lower relative to the CA made using the low sulfur [BMIm]OAc as solvent. Despite the increased temperature and extended contact time, the DS did not increase significantly above that observed after 1.5 h contact time at room temperature regardless of which [BMIm]OAc was used as the solvent. Another notable feature of this example was the color of the solutions and products. The contact solution involving high sulfur [BMIm]OAc solvent was black at all temperatures while the contact solution involving low sulfur [BMIm]OAc solvent retained the straw color typical of these solutions prior to the addition of the anhydride. The CA solids obtained from the high sulfur [BMIm]OAc solvent were brown to black in appearance while the CA solids obtained from the low sulfur [BMIm]OAc solvent were white and provided colorless solutions upon dissolution in an appropriate solvent.

This example shows that impurities (e.g., sulfur or halides) in the high sulfur [BMIm]OAc can act as a catalyst in the esterification of cellulose dissolved in the [BMIm]OAc. However, the same impurities negatively impact the molecular weight and quality of the product in such a manner that the CA does not have practical value. When cellulose is dissolved in [BMIm]OAc containing no or little of these impurities, high-quality CA can be obtained. By introduction of an appropriate catalyst, high quality CA with the desired DS can be obtained in a predictable manner.

Example 24 Acetylation of Cellulose in High Chloride [EMIm]OAc

Cellulose (1.19 g) was dissolved in 22.65 g of commercial [EMIm]OAc which, by XRF, contained 0.463 wt % chloride following the general procedure described in Example 8 with the exception that the mixture was not homogenized prior to heating to 80° C.

To the mechanically stirred straw colored solution preheated to 80° C. was added a solution of MSA (141 mg) and acetic anhydride (3.76 g, 5 eq/AGU) dropwise (10 min). By the end of the addition, the contact mixture became dark brown-black. The contact solution was stirred for 2.5 h before pouring into H₂O. The resulting solids were isolated by filtration, washed extensively with H₂O, and dried overnight at 50° C., 5 mm Hg. This yielded 1.57 g of a brown-black CA powder. Analysis revealed that the CA had a DS of 2.21 and that the Mw was 42,206.

This example shows that [EMIm]OAc containing high levels of halides is not a suitable solvent for esterification of cellulose.

Example 25 Acetylation of Cellulose in [BMIm]Cl and [BMIm]OAc

25A:

Previously dried cellulose (13.2 g) and solid [BMIm]Cl (250.9 g, mp=70° C.) were combined in a glass jar. The glass jar was placed in a preheated 40° C. vacuum oven and heated to 80° C. over 3 h. The sample was allowed to stand under vacuum at 80° C. for ca. 14 h before the jar was removed. The sample was immediately homogenized giving a clear solution of cellulose.

To a 100 mL 3-neck round bottom flask was added 33.6 g of the cellulose solution prepared above. The flask was placed in a preheated 80° C. oil bath and a vacuum was applied (7-8 mm Hg). The solution was then stirred for 21 h while at 80° C. and under vacuum. The cellulose solution was then allowed to cool to 38° C.; the temperature could not be lowered further due to the solution viscosity. Acetic anhydride (5.3 g, 5 eq/AGU) was added dropwise over 7 min. The contact mixture was then stirred at 32-35° C. for 2 h before a small amount of the solution was removed and poured into MeOH resulting in precipitation of the cellulose acetate. The remaining contact mixture was then heated to 50° C. and held at that temperature for 1.6 h before removing a small amount of the solution which was poured into MeOH to precipitate the cellulose acetate. The remaining contact mixture was then heated to 80° C. and held at that temperature for 1.5 h before allowing the solution to cool and adding 60 mL of MeOH to precipitate the cellulose acetate. All three samples were washed extensively with MeOH then dried at 50° C., 5 mm Hg overnight.

25B:

To a 100 mL 3-neck round bottom flask was added 31.3 g of the cellulose solution prepared above. The same general protocol as used in the previous reaction was followed with the exception that Zn(OAc)₂ (0.05 eq/AGU) was added to the cellulose solution prior to cooling to 38° C.

25C:

To a 100 mL 3-neck round bottom flask was added 27.41 g of low sulfur [BMIm]OAc liquid (cf. example 16) and 1.44 g of cellulose. The flask was placed in a preheated 80° C. oil bath and the mixture was allowed to stir overnight (ca. 14 h) under a 2 mm Hg vacuum.

After cooling the solution to room temperature (25.1° C.), Ac₂O (5 eq/AGU) was added to the cellulose solution dropwise (25 min addition). The contact mixture was stirred for 1.8 h at room temperature before removing a small portion of the solution which was poured into MeOH to precipitate the cellulose acetate. The remaining contact mixture was heated to 50° C. and maintained at that temperature for 1.5 h before removing a small portion of the solution which was poured into MeOH to precipitate the cellulose acetate. The remaining contact mixture was heated to 80° C. and maintained at that temperature for 2.5 h before cooling and pouring into MeOH. All three samples were washed extensively with MeOH then dried at 50° C., 5 mm Hg overnight.

25D:

To a 100 mL 3-neck round bottom flask was added 25.55 g of low sulfur [BMIm]OAc liquid (cf. example 16) and 1.35 g of cellulose. The flask was placed in a preheated 80° C. oil bath and the mixture was allowed to stir overnight (ca. 14 h) under a 2 mm Hg vacuum. The same general protocol as used in the previous reaction was followed with the exception that Zn(OAc)₂ (0.05 eq/AGU) was added to the cellulose solution prior to cooling to room temperature.

Analysis of the cellulose acetates isolated from these 4 comparative reactions (25A-25D) is summarized below in Table 7.

TABLE 7 Physical properties of CA prepared in [BMIm]Cl or [BMIm]OAc Entry Solvent Catalyst DS Mn Mw Mz 25A-RT [BMIm]Cl none 0.57 7753 16777 32019 25A-50° C. [BMIm]Cl none 1.42 9892 19083 33019 25A-80° C. [BMIm]Cl none 2.27 11639 21116 34138 25B-RT [BMIm]Cl Zn(OAc)₂ 1.77 8921 19468 36447 25B-50° C. [BMIm]Cl Zn(OAc)₂ 2.32 7652 18849 38367 25B-80° C. [BMIm]Cl Zn(OAc)₂ 2.75 7149 18964 38799 25C-RT [BMIm]OAc none 1.17 7039 41534 118265 25C-50° C. [BMIm]OAc none 1.17 7839 45116 136055 25C-80° C. [BMIm]OAc none 1.17 7943 48559 165491 25D-RT [BMIm]OAc Zn(OAc)₂ 2.27 8478 47730 125440 25D-50° C. [BMIm]OAc Zn(OAc)₂ 2.30 11017 53181 136619 25D-80° C. [BMIm]OAc Zn(OAc)₂ 2.34 12096 56469 141568

This comparative example illustrates a number of important points. In the case of [BMIm]Cl, the DS of the cellulose acetate increases with each contact time-temperature from 0.57 to 2.27. The same trend is observed with [BMIm]Cl+Zn(OAc)₂ with the exception that the DS at each contact time-temperature is higher due to the Zn(OAc)₂ which acts as a catalyst. In the case of [BMIm]OAc, with or without Zn(OAc)₂, the DS does not significantly change from that obtained at room temperature with increasing contact time-temperature; the total DS is significantly increased by the action of the Zn(OAc)₂. This unexpected observation indicates that acetylation of cellulose dissolved in [BMIm]OAc is much faster at lower temperatures relative to that observed in acetylation of cellulose dissolved in [BMIm]Cl. It should also be noted that a transition metal like Zn is very effective in catalyzing or promoting the acylation of cellulose dissolved in ionic liquids. Finally, it should also be noted that the molecular weights of the cellulose acetates obtained by acetylation of cellulose dissolved in [BMIm]OAc is significantly greater relative to when cellulose is dissolved in [BMIm]Cl.

Example 26 Preparation of Mixed Cellulose Esters

The following general procedure was used to prepare cellulose mixed esters. To a 100 mL 3-neck round bottom flask was added the desired amount of 1-butyl-3-methylimidazolium carboxylate. While stirring at room temperature, 5 wt % cellulose was slowly added to the ionic liquid. After the cellulose was dispersed in the ionic liquid, the flask was placed under vacuum (2-5 mm Hg) and the contact mixture was heated to 80° C. The contact solution was then stirred for ca. 2 h before adding 0.1 eg/AGU of Zn(OAc)₂. The contact solution was stirred for ca. 30 min before the solution was allowed to cool to room temperature and stand overnight (ca. 14 h).

The contact solution was placed under N₂ before the dropwise addition of 5 eq/AGU of the desired carboxylic anhydride. When the addition was complete, the flask was placed in a preheated 40° C. oil bath. The contact mixture was stirred for 5 h before the solution was allowed to cool and poured into MeOH. The resulting solids were isolated by filtration, washed extensively with MeOH, and dried in vacuo (50° C., 5 mm Hg). The products were characterized by ¹H NMR and the results are summarized below in Table 8.

TABLE 8 Cellulose Esters Prepared in Different Alkyl Imidazolium Carboxylates Entry Ionic liquid Anhydride DS_(Total) DS_(Ac) DS_(Pr) DS_(Bu) 1 [BMIm]OAc Bu₂O 2.40 2.43 — 0.45 2 [BMIm]OBu Ac₂O 2.43 2.30 — 0.70 3 [BMIm]OPr Bu₂O 2.52 — 1.95 1.05

Note that in Table 8, above, the DS of the individual substituents have been normalized to 3.0 for comparison purposes. As this example illustrates, when cellulose is dissolved in an alkyl imidazolium carboxylate and contacted with an carboxylic anhydride different from the anion of the ionic liquid, the product is a cellulose mixed ester. That is, the cellulose substituents come from the added anhydride and from the alkyl imidazolium carboxylate. In effect, the alkyl imidazolium carboxylate is acting as an acyl donor.

Example 27 Removal of Carboxylic Actid

To each vessel of a 4 vessel Multimax high pressure reactor equipped with an in situ infrared probe was added previously dried [BMIm]OAc, 1 molar equivalent of acetic acid based on ionic liquid, different molar amounts of MeOH based on acetic acid, and optionally, a catalyst (2 mol %). The pressure in each vessel was increased to 5 bar over a 3 min period before the contact temperature was increased to 140° C. over a 25 min period. The contact mixtures were then held at 140° C. for 10-15 h and the reaction in each vessel was monitored by infrared spectroscopy. The vessels were allowed to cool to 25° C. over a 30 min period. The contents of each vessel were then concentrated invacuo to remove all volatile components before analyzing each sample by proton NMR. FIG. 16 shows a plot of wt % acetic acid versus time as determined by infrared spectroscopy; the final concentration of acetic acid was confirmed by ¹H NMR. FIG. 16 shows that in all cases, the reactions were complete within 9-10 h. The most significant factor affecting the rates and extend of reaction was the number of molar equivalents of MeOH. The wt % acetic acid remaining in the [BMIm]OAc ranged from 7.4 wt % to 2.2 wt %.

With typical distillation techniques, it is extremely difficult to get the excess carboxylic acid concentration below 1 molar equivalent based on carboxylated ionic liquid. In the case of acetic acid in [BMIm]OAc, this corresponds to ca. 23 wt % acetic acid. This example shows that, by conversion of the acetic acid to methyl acetate which is much more easily removed, the amount of residual acetic acid can be reduced well below 23 wt %. The amount of acetic acid removed will depend upon the amount of acetic acid initially present, concentration of MeOH, contact times, and contact temperature. As shown in this example, it is not necessary to remove all of residual carboxylic acid; in many instances, it is desirable to have residual carboxylic acid.

Example 28 Solubility of Cellulose in Ionic Liquid

Samples of 1-butyl-3-methylimidazolium acetate containing different amounts of acetic acid in 2 oz jars were dried at 80° C.±°5, ca. 3 mm Hg overnight (ca. 14 h). Examples 28-1 through 28-5 were prepared by the method of Example 27. Examples 28-6 through 28-8 were prepared by adding a known amount of acetic acid to neat [BMIm]OAc (Table). Cellulose (5 wt %, DP 335), was added to each [BMIm]OAc sample and the each sample was briefly homogenized. Each sample was transferred to a microwave reaction vessel which was then capped with an air tight lid then placed in a 48 cell microwave rotor. The rotor was placed in a Anton Paar Synthos 3000 microwave and the cellulose-[BMIm]OAc mixtures were heated to 100° C. using a 3 min ramp and held for 10 min before heating to 120° C. using a 3 min ramp and held for 5 min. Inspection of each vessel indicated that the cellulose in each example was dissolved in the [BMIm]OAc.

TABLE 9 Solubility of Cellulose in [BMIm] OAc Example wt % HOAc IL (g) Soluble 28-1 2.2 6.16 y 28-2 2.8 8.78 y 28-3 5.8 8.48 y 28-4 6.6 8.48 y 28-5 7.4 8.15 y 28-6 10.0 10.23 y 28-7 12.5 10.26 y 28-8 14.5 10.18 y

This example shows that excess residual carboxylic acid in ionic liquids can be reduced by the method of Example 27 and that the recycled ionic liquid can then be used to dissolve cellulose so that the solutions can be used for preparing cellulose esters. This example also shows that cellulose can be dissolved in an ionic liquid containing up to about 15 wt % carboxylic acid.

Example 29 Recycling of Ionic Liquid

To a 500 mL flat bottom kettle was added 299.7 g of [BMIm]OAc. A 4-neck top was placed on the kettle and the kettle was fitted with a N₂/vacuum inlet, a React IR 4000 diamond tipped IR probe, a thermocouple, and for mechanical stirring. The kettle contents were placed under vacuum (ca. 4.5 mm Hg) and heated to 80° C. using an oil bath. The removal of water from the [BMIm]OAc was followed by infrared spectroscopy (FIG. 17). After ca. 16 h, the oil bath was removed and the kettle contents were allowed to cool to room temperature.

To the ionic liquid was added 3.77 g of Zn(OAc)₂. The mixture was stirred for ca. 75 minutes to allow the Zn(OAc)₂ to dissolve before slowly adding 33.3 g (10 wt %) of previously dried cellulose (DP ca. 335) over a 26 min period. The mixture was stirred at room temperature for ca. 4 h at which time no particles or fiber were visible in the translucent solution; infrared spectroscopy indicated that all of the cellulose was dissolved (FIG. 18). The solution was heated to 80° C. By the time the temperature reached 60° C., the translucent solution was completely clear. After reaching 80° C., the solution was cooled to room temperature.

To the cellulose-[BMIm]OAc solution was added 104.9 g of Ac₂O (5 eq) dropwise over a 70 min period. During the Ac₂O addition, the contact temperature rose from an initial value of 21.4° C. to a maximum value of 44.7° C. Infrared spectroscopy indicated that the Ac₂O was consumed nearly as fast as it was added (FIG. 19). When all of the Ac₂O was added, the contact temperature immediately began to decline and the contact mixture went from a fluid liquid to a flaky gel. Stirring was continued for an additional 3.5 h but no changes were observed by infrared spectroscopy.

The gel was then added to 800 mL of MeOH while stirring resulting in the precipitation of a white powder. After separation by filtration, the solids were then washed 3 times with ca. 800 mL portions of MeOH then 1 time with ca. 900 mL of MeOH containing 11 wt % of 35 wt % H₂O₂. The solids were then dried at 40° C., 3 mm Hg resulting in 60.4 g of a white solid. Analysis by proton NMR and GPC revealed that the solid was a cellulose triacetate (DS=3.0) having a Mw of 58,725. The cellulose triacetate (13.6 wt %) was completely soluble in 90/10 CH₂Cl₂/MeOH from which clear films can be cast. Such films are useful in constructing liquid crystalline displays and in photographic film base.

The precipitation and wash liquids from the cellulose triacetate isolation were concentrated invacuo at 50° C. until the vacuum dropped to ca. 3 mm Hg which gave 376.6 g of a liquid. Proton NMR showed that the liquid was [BMIm]OAc containing ca. 17 wt % excess acetic acid. To a 1.8 L autoclave was added the 376.8 g of recovered [BMIm]OAc along with 483.8 g of MeOH. The pressure in autoclave was adjusted to 100 psi with N₂ before the vessel contents were heated to 140° C. and held for 9 h. After cooling to room temperature, the volatile components were removed invacuo which gave 299.8 g of a liquid. Proton NMR showed the liquid to be [BMIm]OAc containing 2.6 wt % excess acetic acid. When the weight of the initial [BMIm]OAc is corrected for water content, the amount of recycled [BMIm]OAc corresponds to 100% recovery.

This example shows that cellulose triacetate can rapidly be prepared from cellulose dissolved in ionic liquids. This example also shows that excess carboxylic acid can be removed from the ionic liquid and the recycled ionic liquid can be recovered in high yield. The recycled ionic liquid can then be used to dissolve cellulose so that the solutions can be used again for preparing cellulose esters.

Example 30 Anion Exchange to Form Carboxylated Ionic Liquid

To a vial containing a small magnetic stir bar was added 4.2 g of [BMIm]formate. An iC10 diamond tipped IR probe was inserted into the vial so that the reaction could be monitored in situ by infrared spectroscopy. To the [BMIm]formate was added 0.5 eq of Ac₂O in one portion. As FIGS. 20 and 21 show, 50% of the [BMIm]formate was immediately converted to [BMIm]OAc. Additional spectra were collected to allow the system to stabilize before adding another 0.5 eq of Ac₂O in one portion. Infrared spectroscopy indicated that the remaining [BMIm]formate was immediately converted to [BMIm]OAc.

This example shows that [BMIm]formate is rapidly converted to [BMIm]OAc with the addition of Ac₂O. The reaction rate is so rapid that the [BMIm]formate can be titrated with Ac₂O until no gas is evolved.

Example 31 Effect of MeOH During Anion Exchange

To a vial containing a small magnetic stir bar was added 3.15 g of [BMIm]formate. An iC10 diamond tipped IR probe was inserted into the vial so that the reaction could be monitored in situ by infrared spectroscopy. To the [BMIm]formate was added 2 eq of MeOH. After the system thermally stabilized, 1 eq of Ac₂O was added to the [BMIm]formate in one portion. As FIGS. 22 and 23 show, infrared spectroscopy indicated that the [BMIm]formate was immediately converted to [BMIm]OAc.

This example shows that the reaction of [BMIm]formate with Ac₂O to form [BMIm]OAc is much faster than the reaction of Ac₂O with MeOH to form MeOAc. Hence, it is not necessary to remove MeOH from [BMIm]formate prior to converting the [BMIm]formate to [BMIm]OAc.

Example 32 Effects of Water Modification and MSA

A 3-neck 250 mL round bottom flask, fitted with two double neck adapters giving five ports, was equipped for mechanical stirring, with a iC10 diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added 62.37 g of 1-butyl-3-methylimidazolium acetate.

To 5.06 g (7.5 wt %) of cellulose (DP ca. 335) was added 20.68 g of water. After hand mixing, the cellulose was allowed to stand in the water for 65 min at 60° C. before filtering which, gave 10.78 g of a wet cellulose cake. The water wet cellulose was then added in small portions to the [BMIm]OAc (5 min addition). Within 5 min, the cellulose was well dispersed in the ionic liquid (a few small clumps were visible). The mixture was stirred for 7 min before a preheated 80° C. oil bath was raised to the flask. The mixture was then stirred for 28 min (visually, nearly all of the cellulose was dissolved) before slowly placing the flask contents under vacuum with the aid of a bleed valve (FIG. 24). After 1.5 h, the vacuum was 1.9 mm Hg. The clear mixture was then stirred overnight under vacuum at 80° C.

The clear solution was allowed to cool to room temperature 15 h 45 min from the point of cellulose addition before adding a mixture of 12.11 g (3.8 eq) of Ac₂O and 600 mg of MSA dropwise (28 min addition). The maximum temperature reached during the Ac₂O addition was 46° C. Eight minutes after completing the Ac₂O addition, a preheated 50° C. oil bath was raised to the flask. The mixture was stirred for 16 min before 1.46 g of water was slowly added to the solution (2 min addition). The solution was then stirred for 17 min before adding an additional 0.47 g of water. The solution was then stirred for 5 h 9 min before cooling the solution to room temperature. The reaction was sampled (FIG. 25) throughout the contact period by removing 6-10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed once with a 100 mL portion of MeOH then twice with 100 mL of MeOH containing 8 wt % of 35 wt % H₂O₂. The samples were then dried at 60° C., 5 mm Hg overnight.

This example illustrates a number of benefits of the methods employed herein. As can be seen from FIG. 24, water wet cellulose can be readily dissolved in carboxylated ionic liquid even when a significant amount of water still remains in the ionic liquid. As shown in FIG. 25, the rate of reaction in the acylation of this cellulose in a carboxylated ionic liquid is very rapid; a significant concentration of Ac₂O is never observed indicating that the Ac₂O is consumed as fast as it is added. The rapid rates of reaction can lead to a much different monomer distribution relative to that observed in other ionic liquids. For example, FIG. 26 compares the proton resonances of the protons attached to the anhydroglucose rings of cellulose acetates (DS=2.56) prepared from cellulose dissolved in [BMIm]OAc (top spectrum) and dissolved in [BMIm]Cl (bottom spectrum). The major resonances in the top spectrum centered near 5.04, 5.62, 4.59, 4.29, 4.04, 3.73, and 3.69 correspond to trisubstituted monomers. In the bottom spectrum, there are much less of these resonances relative to the other type of monomer resonances. This discovery is significant in that the rapid rates of reaction provide a means to produce nonrandom cellulose ester copolymers with different levels of block segments. The extent and the size of the block segments will depends upon factors such as mixing, prior water treatment or no water treatment of the cellulose, concentration and type of catalyst, contact temperature, and the like. As shown in FIG. 24, 3 samples were taken prior to the addition of water. These 3 samples ranged in DS from 2.48-2.56 and at 10 wt % in acetone, they were soluble giving slightly hazy solutions (solubility rating of 2). In contrast, the 2 samples taken after water addition (DS ca. 2.52) were insoluble in acetone (solubility rating of 6). FIG. 27 compares the ring proton resonances for cellulose acetates prepared from cellulose dissolved in [BMIm]OAc before and after addition of water. The top spectrum corresponds to a cellulose acetate after water addition (DS=2.53) and the bottom spectrum corresponds to a cellulose acetate before water addition (DS=2.56). The differences between these 2 spectra are consistent with different monomer compositions in the copolymers.

Example 33 Production of Cellulose Triacetate

To a 3-neck 100 mL round bottom flask equipped for mechanical stirring and with an N₂/vacuum inlet added 34.63 g of 1-ethyl-3-methylimidazolium acetate. While stirring rapidly, added 6.11 g (15 wt %) of dry cellulose powder (DP ca. 335). The flask was placed in a 90° C. oil bath and the mixture was stirred for 10 min before applying vacuum (2 mm Hg). After 50 min, the oil bath temperature was increased to 100° C. After 2 h 25 min, the oil bath was turned off and left the solution was left standing under vacuum overnight.

To the cellulose solution was added a mixture of 731 mg of MSA and 19.24 g (5 eq) of Ac₂O dropwise. Initially, the solution was stirred slowly so that the solution did not bunch around the stir shaft. As the Ac₂O was added, the solution viscosity dropped; after adding ca. 5 mL, the solution stirred easily and the stir rate was increased. During the addition, the solution viscosity did not increase and no localized gels were observed until the last few drops of Ac₂O were added (40 min addition). At this point the entire contact mixture suddenly gelled. The contact temperature rose from 24.1° C. to 47.5° C. by the end of addition. During the addition, there was little change in the color of the solution. After the reaction gelled, 11.54 g of the reaction mixture was removed with a spatula and solids were obtained by precipitation in MeOH (Sample 1). The flask containing the remaining reaction mixture was then placed in a preheated 50° C. oil bath. After 20 min at 50° C., there was no evidence of the gel softening. Hence, the gel was allowed to cool to room temperature and 50 mL of MeOH was added to the flask. The flask contents were then dumped into 400 mL of MeOH which gave a white precipitate (Sample 2). Both fractions were processed by stirring the initial slurry for ca. 1 h before isolating the solids by filtration. The solids were washed by taking them up in 300 mL of MeOH and stirring the slurry for ca. 1 h before the solids were isolated by filtration. The solids were twice taken up in 300 mL of 12/1 MeOH/35% H₂O₂ and the slurry was stirred for ca. 1 h before the solids were isolated by filtration. The solids were then dried overnight at 50° C., ca. 20 mm Hg.

The combined yield for Sample 1 and 2 was 10.2 g of a white solid. Analysis by ¹H NMR showed that Samples 1 and 2 were identical and that they were cellulose triacetates with a DS of 3.0. By GPC, both samples have a Mw of ca. 54,000.

This example shows that cellulose triacetate can rapidly be prepared from cellulose dissolved in [EMIm]OAc. Cellulose triacetate can be used to prepare film useful in liquid crystalline displays and photographic film base.

Example 34 Immiscible Co-Solvent (Effect on IL Viscosity)

To a 3-neck 50 mL round bottom flask equipped for mechanical stirring and with an N₂/vacuum inlet added 20.03 g of 1-ethyl-3-methylimidazolium acetate. While stirring rapidly, added 1.05 g of dry cellulose powder (DP ca. 335). The flask was placed under vacuum (2 mm Hg) and placed in an oil bath preheated to 90° C. After 1 h 45 min, the oil bath temperature was increased to 100° C. and stirred an additional 55 min (2 h 40 min total contact time) before allowing the solution to cool to ambient temperature while under vacuum.

To the cellulose solution was added 20 mL of methyl acetate resulting in a 2-phase reaction mixture. While stirring rapidly, a mixture of 131 mg of MSA and 4.63 g of Ac₂O was added drop wise (10 min). The contact temperature increased from 23.3° C. to 35.4° C. and, at the end of the addition, the contact mixture was a single phase and the viscosity of the single phase was much less than that of the original cellulose-[EMIm]OAc solution. Twenty-five minutes after beginning the addition, the flask was placed in a preheated 50° C. oil bath. The contact mixture was stirred for 2 h at 50° C. before allowing the contact mixture to cool to ambient temperature over 50 min. The product was precipitated in 350 mL of MeOH and the slurry was stirred for ca. 1 h before the solids were isolated by filtration. The solids were washed by taking them up in 300 mL of MeOH and stirring the slurry for ca. 1 h before the solids were isolated by filtration. Twice, the solids were taken up in 300 mL of 12/1 MeOH/35% H₂O₂ and the slurry was stirred for ca. 1 h before the solids were isolated by filtration. The solids were then dried overnight at 50° C., ca. 20 mm Hg which gave 1.68 g of a white solid. Analysis by ¹H NMR revealed that the solid was a cellulose acetate with a DS of 2.67. Analysis by GPC indicated that the cellulose acetate had a Mw of 51,428 and a Mw/Mn of 4.08.

This example shows that a cellulose solution in an ionic liquid can be contacted with an immiscible or sparingly soluble co-solvent without causing precipitation of the cellulose. Upon contact with an acylating reagent, the cellulose is esterified changing the solubility of the now cellulose ester-ionic liquid solution with the formerly immiscible co-solvent so that the contact mixture becomes a single phase. The resulting single phase has much lower solution viscosity than the initial cellulose-ionic liquid solution. This discovery is significant in that highly viscous cellulose solutions can be used to make cellulose esters while still maintaining the ability to mix and process the solution. The discovery also provides a means to process highly viscous cellulose-ionic liquid solutions at lower contact temperatures. The cellulose ester product can be isolated from the new single phase by conventional means. The cellulose ester product has desirable degrees of substitution, molecular weights, and solubility in solvents such as acetone, and can be readily melt processed when plasticized with plasticizers such as diethyl phthalate and the like.

Example 35 Immiscible Co-Solvent (Biphasic to Single Phase)

A 3-neck 100 mL round bottom flask containing 28.84 g of a 5 wt % cellulose solution in [BMIm]Cl was equipped for mechanical stirring and with an N₂/vacuum inlet. The flask was placed in a preheated 80° C. oil bath and the flask contents were placed under vacuum (ca. 7 mm Hg) for 2 h. To the solution was added 25 mL of methyl ethyl ketone that had been previously dried over 4 A molecular sieves resulting in two well defined phases. To the biphasic mixture was added 4.54 g of Ac₂O while stirring vigorously. After ca. 75 min, the contact mixture appeared to be homogeneous. After 2.5 h, the contact mixture was allowed to cool to room temperature. Phase separation did not occur even when a small amount of water and methyl ethyl ketone was added to the homogeneous mixture. The product was isolated by addition of the contact mixture to 200 mL of MeOH followed by filtration to separate the solids. The solids were washed twice with MeOH and three times with water before they were dried at 50° C., ca. 5 mm Hg. Analysis by ¹H NMR and by GPC revealed that the product was a cellulose acetate with a DS of 2.11 and Mw of 50,157.

This example shows that a cellulose solution in an ionic liquid such as [BMIm]Cl can be contacted with an immiscible or sparingly soluble co-solvent such as methyl ethyl ketone without causing precipitation of the cellulose. Upon contact with an acylating reagent, the cellulose is esterified changing the solubility of the now cellulose ester-ionic liquid solution with the formerly immiscible co-solvent so that the contact mixture became a single phase from which the cellulose ester could be isolated by precipitation with an alcohol.

Definitions

As used herein, the terms “a,” “an,” “the,” and “the” mean one or more.

As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

As used herein, the terms “comprising,” “comprises,” and “comprise” are open-ended transition terms used to transition from a subject recited before the term to one or more elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up the subject.

As used herein, the terms “containing,” “contains,” and “contain” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

As used herein, the terms “having,” “has,” and “have” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

As used herein, the terms, “including,” “include,” and “included” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

Numerical Ranges

The present description uses numerical ranges to quantify certain parameters relating to the invention. It should be understood that when numerical ranges are provided, such ranges are to be construed as providing literal support for claim limitations that only recite the lower value of the range as well as claims limitation that only recite the upper value of the range. For example, a disclosed numerical range of 10 to 100 provides literal support for a claim reciting “greater than 10” (with no upper bounds) and a claim reciting “less than 100” (with no lower bounds).

CLAIMS NOT LIMITED TO SINGLE EMBODIMENT

The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention.

The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims. 

1. A process for making a carboxylated ionic liquid, said process comprising: contacting an alkyl amine formate ionic liquid with an anhydride under conditions sufficient to convert said alkyl amine formate ionic liquid into said carboxylated ionic liquid via anion exchange, wherein said carboxylated ionic liquid contains sulfur in an amount less than 200 ppmw and halides in an amount less than 200 ppmw.
 2. The process of claim 1, wherein said carboxylated ionic liquid contains sulfur in an amount less than 50 ppmw and halides in an amount less than 50 ppmw.
 3. The process of claim 1, wherein said carboxylated ionic liquid contains transition metals in an amount less than 200 ppmw.
 4. The process of claim 1, wherein said carboxylated ionic liquid contains no sulfur and no halides.
 5. The process of claim 1, wherein said carboxylated ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium propionate, 1-ethyl-3-methylimidazolium butyrate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium propionate, 1-butyl-3-methylimidazolium butyrate, and mixtures thereof.
 6. The process of claim 1, wherein the amine of said alkyl amine formate ionic liquid is selected from the group consisting of alkyl substituted imidazolium, alkyl substituted pyrazolium, alkyl substituted oxazolium, alkyl substituted triazolium, alkyl substituted thiazolium, and mixtures thereof.
 7. The process of claim 1, wherein the amine of said alkyl amine formate ionic liquid is alkyl substituted imidazolium.
 8. The process of claim 1, wherein said alkyl amine formate ionic liquid is selected from the group consisting of 1-methyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium formate, 1-propyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium formate, 1-hexyl-3-methylimidazolium formate, 1-octyl-3-methylimidazolium formate, and mixtures thereof.
 9. The process of claim 1, wherein during said contacting at least a portion of the formate of said alkyl amine formate ionic liquid is replaced via anion exchange with a carboxylate anion originating from said anhydride.
 10. The process of claim 1, wherein said anhydride is selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, hexanoic anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauric anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, substituted benzoic anhydrides, phthalic anhydride, isophthalic anhydride, and mixtures thereof.
 11. The process of claim 1, wherein said alkyl amine formate ionic liquid and said anhydride are contacted in a contact mixture containing said anhydride in an amount in the range of from 1 to 20 molar equivalents per alkyl amine formate.
 12. The process of claim 1, wherein said alkyl amine formate ionic liquid and said anhydride are contacted in a contact mixture containing water or alcohol in an amount in the range of from 0.01 to 20 molar equivalents per alkyl amine formate.
 13. The process of claim 1, wherein said contacting is carried out at a temperature in the range of from 0 to 200° C. and a pressure up to 21,000 kPa.
 14. The process of claim 1, wherein said alkyl amine formate ionic liquid and said anhydride are contacted in a contact mixture containing said anhydride in an amount in the range of from 1 to 6 molar equivalents per alkyl amine formate, wherein said contact mixture contains methanol in an amount in the range of from 1 to 10 molar equivalents per alkyl amine formate, wherein said contacting is carried out at a temperature in the range of from 25 to 170° C. and a pressure up to 10,000 kPa.
 15. The process of claim 1, further comprising contacting at least one amine with at least one alkyl formate to thereby produce said alkyl amine formate ionic liquid.
 16. The process of claim 15, wherein said amine is selected from the group consisting of imidazole, pyrazole, oxazole, triazole, thiazole, and mixtures thereof.
 17. The process of claim 16, wherein said alkyl formate comprises methyl formate.
 18. The process of claim 17, wherein said amine is imidazole.
 19. The process of claim 1, further comprising contacting an altered ionic liquid with an alkyl formate to thereby form said alkyl amine formate ionic liquid, wherein said altered ionic liquid originates from a process for producing cellulose ester.
 20. The process of claim 19, wherein said altered ionic liquid comprises at least two different types of anions.
 21. The process of claim 19, wherein said alkyl formate comprises methyl formate. 